Unravelling environmental and economic criteria for resource recovery in centralised and decentralised wastewater treatment

TESE DE DOUTORAMENTO UNRAVELLING ENVIRONMENTAL AND ECONOMIC CRITERIA FOR RESOURCE RECOVERY IN CENTRALISED AND DECENTRALISED WASTEWATER TREATMENT Andrea Arias Cisterna ESCOLA DE DOUTORAMENTO INTERNACIONAL PROGRAMA DE DOUTORAMENTO EN ENXEÑERÍA QUÍMICA E AMBIENTAL SANTIAGO DE COMPOSTELA 2021 DECLARACIÓN DO AUTOR/A DA TESE UNRAVELLING ENVIRONMENTAL AND ECONOMIC CRITERIA FOR RESOURCE RECOVERY IN CENTRALISED AND DECENTRALISED WASTEWATER TREATMENT Dña. Andrea Arias Cisterna Presento a miña tese, seguindo o procedemento axeitado ao Regulamento, e declaro que: 1) A tese abarca os resultados da elaboración do meu traballo. 2) De selo caso, na tese faise referencia ás colaboracións que tivo este traballo. 3) A tese é a versión definitiva presentada para a súa defensa e coincide coa versión enviada en formato electrónico. 4) Confirmo que a tese non incorre en ningún tipo de plaxio doutros autores nin de traballos presentados por min para a obtención doutros títulos. En .........., ... de ..... de 20.. AUTORIZACIÓN DOS DIRECTORES DA TESE UNRAVELLING ENVIRONMENTAL AND ECONOMIC CRITERIA FOR RESOURCE RECOVERY IN CENTRALISED AND DECENTRALISED WASTEWATER TREATMENT Dona María Teresa Moreira Vilar, Catedrática de Enxeñería Química y Don Gumersindo Feijoo Costa, Catedrático de Enxeñería Química INFORMAN: Que a presente tese, correspóndese co traballo realizado por D/Dna. Andrea Arias Cisterna, baixo a miña dirección, e autorizo a súa presentación, considerando que reúne os requisitos esixidos no Regulamento de Estudos de Doutoramento da USC, e que como director desta non incorre nas causas de abstención establecidas na Lei 40/2015. De acordo co indicado no Regulamento de Estudos de Doutoramento, declara tamén que a presente tese de doutoramento é idónea para ser defendida en base á modalidade de Monográfica con reproducción de publicaciones, nos que a participación do/a doutorando/a foi decisiva para a súa elaboración e as publicacións se axustan ao Plan de Investigación. En .........., ... de ..... de 20.. LISTS OF CONTENTS Abbreviations .................................................................................................................. 13 Abstract………………………………………………………………………………………………….15 Resumo ............................................................................................................................... 19 CHAPTER 1. INTRODUCTION 1. General introduction ........................................................................................... 31 1.1. Growing environmental concern about water as a finite resource 31 1.2. Circular economy in the wastewater treatment sector ....................... 33 1.3. New wastewater treatment strategy for centralised systems .......... 35 1.4. Decentralised approach for wastewater treatment ............................. 38 1.5. Life cycle assessment (LCA) methodology and its application to wastewater treatment ............................................................................................. 42 1.6. Economic evaluation ........................................................................................ 46 1.7. Thesis outline: objectives and structure................................................... 48 1.8. References ............................................................................................................ 50 SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS CHAPTER 2. Identifying environmental and economic barriers associated with the scale of operation in the anaerobic digestion process 2.1. Introduction ............................................................................................................. 69 2.2. Materials and methods ......................................................................................... 70 2.2.1. Goal and scope definition ............................................................................ 70 2.2.2. Functional unit ................................................................................................ 71 2.2.3. System boundaries ........................................................................................ 71 2.2.4. Life cycle inventory approach ................................................................... 73 2.2.5. Life cycle impact assessment and interpretation .............................. 76 2.2.6. Economic indicators ..................................................................................... 77 2.3. Results and discussion ......................................................................................... 77 2.3.1. Environmental profile of the different sludge lines .......................... 77 2.3.2. Assessment of the feasibility of the anaerobic digestion (AD) unit .......................................................................................................................................... 80 2.3.3. Energy benefit in the different sludge lines ......................................... 82 2.3.4. Economic analysis of the different sludge lines.................................. 83 2.4. Conclusions ............................................................................................................... 85 2.5. References ................................................................................................................. 85 CHAPTER 3. Benchmarking environmental and economic indicators of sludge management alternatives aimed at enhancing energy efficiency recovery 3.1. Introduction ............................................................................................................. 91 3.2. Materials and methods ......................................................................................... 92 3.2.1. Description of the different sludge lines and scope of the study . 92 3.2.2. Life cycle inventory (LCI) for the different sludge pre-treatments .......................................................................................................................................... 94 3.2.3. Environmental and economic indicators for the sludge pretreatments .................................................................................................................... 99 3.3. Results and discussion ...................................................................................... 100 3.3.1. Main parameters and life cycle results of the different sludge scenarios .................................................................................................................... 100 3.3.2. Economic evaluation of the different sludge pre-treatments .... 106 3.3.3. Sensitivity analysis for the different pre-treatment processes . 108 3.3.4. Evaluation of the efficiency of the different sludge pre-treatments ....................................................................................................................................... 110 3.3.5. How to improve the efficiency of a WWTP ........................................ 110 3.4. Conclusions ............................................................................................................ 112 3.5. References .............................................................................................................. 112 CHAPTER 4. Pursing energy self-sufficient in wastewater treatment plants: environmental and economic assessment of innovative options 4.1. Introduction .......................................................................................................... 121 4.2. Materials and methods ...................................................................................... 123 4.2.1. Description of the wastewater schemes and scope of the study 123 4.2.2. Inventory data acquisition for the new wastewater configurations ....................................................................................................................................... 128 4.2.3. Impact assessment methodology and economic evaluation....... 132 4.3. Environmental and economic results .......................................................... 132 4.3.1. Environmental and economic approach for the four studied scenarios .................................................................................................................... 132 4.3.2. Environmental perspective for each wastewater treatment configuration ............................................................................................................ 136 4.4. Discussion .............................................................................................................. 140 4.4.1. Improving wastewater treatment efficiency in the WWTPs ....... 140 4.4.2. How conventional and new technologies influence the effluent quality ..................................................................................................................... 1422 4.4.3. Economic aspects focused on energy recovery ................................ 143 4.4.4. Sensitivity analysis of the functional unit (FU) ................................ 144 4.5. Conclusions ............................................................................................................ 145 4.6. References .............................................................................................................. 145 CHAPTER 5. Mapping the environmental and economic impacts of innovative technologies for enhancement of biogas production and sludge management in wastewater systems 5.1. Introduction .......................................................................................................... 155 5.2. Materials and methods ...................................................................................... 156 5.2.1. Methodology on simulation and environmental assessment ..... 156 5.2.2. Goal and scope of the two wastewater schemes considered ...... 159 5.2.3. System boundaries for the wastewater treatment configurations ....................................................................................................................................... 160 5.2.4. Inventory data acquisition through the simulation process ...... 162 5.2.5. Environmental and economic indicators selected for the case studies ......................................................................................................................... 168 5.3. Results ..................................................................................................................... 169 Subsequently, the wastewater line was modified (Chapters 4 and 5). A strategy based on organic matter (OM) recovery in primary treatment and nitrogen removal in secondary treatment by partial nitrificationanammox was compared with a conventional approach. In Chapter 4, a virtual plant designed for 100.000 population equivalents with different schemes based on the above-mentioned strategy was evaluated. The three innovative schemes are: (i) upflow anaerobic sludge blanket (UASB) followed by an integrated fixed activated sludge (IFAS), (ii) high rate activated sludge (HRAS) + IFAS, and, (iii) rotating belt filter (RBF) + chemically enhanced primary treatment (CEPT) + IFAS. These schemes were compared with a primary clarifier (PC) followed by a conventional activated sludge (CAS) with nitrogen removal. The main objectives are to study energy production, effluent quality and sludge production and how these factors can affect the environmental and economic profile of the wastewater line. Finally, in Chapter 5, the schemes were virtually modelled in two real plants located in Denmark and Spain. The existing configuration was replaced by two schemes: (i) HRAS + IFAS and (ii) Enhanced Rotating Belt Filter (ERBF) + IFAS. In this way, the main inputs and outputs of the different systems were estimated to calculate the environmental and economic profile. Finally, this section will conclude with the up-scale of a technology for nitrogen removal in the side stream (Chapter 6). The main objective is to establish the minimum scale to reliably estimate the environmental and economic indicators. In this way, the study can help as a guideline to address the evaluation of smaller units such as those of decentralized systems. The second section of this thesis “changing the paradigm of wastewater treatment” seeks to highlight the importance of decentralised systems for resource recovery focusing on energy and water with the aim of demonstrating environmental and economic benefits. This section consists of two chapters (Chapter 7 and 8). The main objective of Chapter 7 is to evaluate the performance of a membrane plant for the recovery of irrigation water in Turkey. The wastewater plant is designed for 2,000 equivalent inhabitants. In this Chapter, an indicator called AWARE (available remaining water method) was applied to measure the water scarcity and the benefits of water reuse. Finally, Chapter 8 compares the approaches of decentralised and centralised systems from a citizen perspective. The study aims to analyse the decrease or increase in water consumption and carbon footprint of a citizen living in a neighbourhood that incorporates a decentralized or centralized wastewater treatment system. Keywords: energy production, innovative technologies, decentralised wastewater, economic indicators, life cycle assessment (LCA), reclaimed water RESUMO RESUMO 19 RESUMO Durante os últimos anos, a poboación mundial experimentou un crecemento substancial e prevese que esta tendencia continúe. Isto implica que se deban xerar máis alimentos, enerxía ou auga potable, entre outros bens para satisfacer ás necesidades de dita poboación. Non obstante, o consumo de máis recursos implica unha xeración maior de residuos como, por exemplo, plásticos, augas residuais, desperdicios alimentarios, etc. Estes residuos deben ser tratados correctamente para evitar problemas relacionados coa contaminación do medio ambiente. No tratamento de residuos, as plantas de tratamento de augas residuais son factores chave para garantir a redución da descarga de contaminantes ó medio, xa que, se non son xestionadas correctamente, poden causar graves problemas ambientais e incluso a mortaldade das especies que viven nel. Así mesmo, estas plantas de tratamento deben facer fronte a novos desafíos como a eliminación de contaminantes cada vez máis complexos tales como fármacos, hormonas ou fragrancias sendo cada vez máis sustentables dende o punto de vista económico, ambiental e social. Neste contexto, o termo residuo debe ser substituído pola palabra produto. Polo tanto, as depuradoras deben traballar non para eliminar recursos senón para recuperalos, é o que se coñece como pensamento de economía circular. De esta maneira, o que se consegue é transformar ás xestoras de residuos en biorefinerías. O que se pretende nesta tese é abordar este cambio a través de diversas configuracións e distintos esquemas de tratamentos. Para abordar este cambio, a tese foi dividida en dúas seccións, as cales vanse explicar a continuación. Capítulo 1: Introdución. Este primeiro capítulo pretende servir como marco teórico e explicar o motivo principal polo cal se decidiu realizar esta tese. O marco teórico engloba a problemática actual relacionada cos problemas de contaminación de augas, cambio climático ou aumento da poboación, entre outros. Definiuse o concepto de economía circular e como englobar ás depuradoras dentro deste termo, así como as estratexias que se poden levar a cabo para conseguir este propósito. Estes sistemas poden estar formados por distintas tecnoloxías que teñen distintas funcións dependendo da súa aplicación. RESUMO 20 Como un dos obxectivos desta tese é abordar a parte ambiental e económica de distintos tratamentos de auga, describíronse en detalle as distintas ferramentas e indicadores que se poden empregar para este fin. Ademais, estudouse o que levan feito outros autores no ámbito das augas residuais en combinación con criterios ambientais e económicos. Dita información recóllese nunha revisión bibliográfica que se inclúe dentro deste capítulo. Finalmente, para concluír este primeiro capítulo, resumíronse os obxectivos que persegue cada capítulo que forma esta tese. A primeira sección da tese titulada “melloras para sistemas centralizados” recolle un total de 5 capítulos. Esta parte do traballo foi financiada por un proxecto chamado Pioneer_STP (polas súas siglas en inglés The Potential of Innovative Tecnologies to Improve Sustainability of Sewage Treatment Plants), o cal ten como obxectivo principal, avaliar os desafíos relacionados co tratamento das augas residuais dende un punto de vista holístico que se centra en conceptos como a recuperación de enerxía, a xestión de lodos, a redución de custos e a mellora da calidade dos efluentes en sistemas centralizados de auga. Para cumprir con estes propósitos, propuxéronse e analizáronse novos esquemas de tratamento de augas. Ditos esquemas foron avaliados dende un punto de vista económico e ambiental durante esta tese (dende o capítulo 2 ata o 6). A información contida nestes capítulos, así como os principais resultados explícanse a continuación. Capítulo 2. Avaliar as barreiras ambientais e económicas asociadas co escalado da dixestión anaerobia. Este capítulo centrouse na avaliación da dixestión anaerobia para distintos tamaños de plantas reais de tratamento. Analizáronse catro liñas de lodos situadas en distintas localidades de España que van dende os 25.000 habitantes equivalentes (a máis pequena) ata 1.000000 habitantes equivalentes. A principal diferenza é que a liña máis pequena non ten dixestión anaerobia mentres que as outras tres configuracións de lodos si que dispoñen desta unidade. O principal obxectivo foi definir a escala de planta de tratamento a partir da cal convén configurar a tecnoloxía da dixestión anaerobia dacordo con criterios ambientais e RESUMO 21 económicos, así como, identificar as barreiras existentes que impiden unha implantación xeneralizada. Os resultados deste traballo indicaron que esta tecnoloxía axuda a reducir os impactos ambientais e custos económicos debido á recuperación enerxética a través do biogás. A planta de tratamento que non ten dixestión anaerobia presentou custos de operación máis elevados relacionados co consumo enerxético e de químicos. Ademais, non se obtivo ningún beneficio ambiental asociado á recuperación enerxética. Cando a tecnoloxía se incorporou nesta liña obtivéronse beneficios non só ambientais senón tamén económicos. Se ben é certo, ó incorporar a unidade a complexidade tecnolóxica incrementa. Así mesmo, están as limitacións relacionadas co seu rendemento. Unha opción para mellorar este rendemento é a introdución de residuos orgánicos ou agrícolas no propio dixestor. Non obstante, a dixestión anaerobia considérase un proceso lento debido a hidrólise (primeira etapa deste proceso). Polo tanto, hoxe en día búscanse solucións tecnolóxicas para acelerar este paso. Estas solucións así como da súa problemática estudáronse no capítulo 3. Capítulo 3. Avaliación comparativa dos indicadores ambientais e económicos das alternativas de xestión de lodos destinadas a mellorar a eficiencia enerxética e a recuperación de nutrientes. Como se dixo anteriormente, o papel da xestión de lodos xoga un papel importante dentro do esquema de tratamento. Polo tanto, a finalidade deste estudo foi analizar alternativas para acelerar a etapa de hidrólise, mellorar a degradabilidade do lodo e incrementar a produción de enerxía. Para este propósito, estudáronse dous pre-tratamentos de lodos: i) o primeiro baseouse na adición de químicos e outro ii) fundamentouse no incremento de presión e temperatura (proceso termal) para xerar estas melloras. As novas propostas comparáronse cun sistema convencional (sen pre-tratamento de lodos). Tamén, se incluíron na análise dous tipos de tratamentos finais dos lodos: i) aplicación á agricultura e ii) incineración. O sistema convencional mostrou unha xeración enerxética menor e unha cantidade de lodo maior en comparación coas liñas de lodos que RESUMO 22 incorporaron o tratamento químico e termal. Polo tanto, estas últimas obtiveron un perfil ambiental menor. En termos de custos, os pretratamentos asomaron custos maiores relacionados coa fase de construción pero que poden ser amortizados máis rápido debido á produción enerxética. A pesar de que no proceso termal hai máis consumo enerxético que no químico, o lodo está libre de patóxenos e pode ser aplicado á agricultura directamente. Isto implica unha redución maior en custos de operación. Con respecto ó tratamento final dos lodos, a aplicación á agricultura presentou mellores impactos, aínda que se debe prestar atención á concentración de metais pesados e microcontaminantes, xa que en grandes cantidades poden presentar un problema de contaminación do medio no que se aplican. Unha vez estudada a liña de lodos dos sistemas centralizados, o seguinte paso foi propor modificacións en toda a planta de tratamento (liña de augas e lodos). As tecnoloxías usadas para este fin definíronse nos capítulos 4 e 5. Capítulo 4: Procura da eficiencia enerxética nas plantas de augas de tratamento: avaliación ambiental e económica de opcións innovadoras Os esquemas de tratamento estudados durante este capítulo baseáronse nunha nova estratexia de tratamento das augas que consiste na recuperación de materia orgánica no tratamento primario e a eliminación do nitróxeno mediante un proceso de nitrificación parcial-anammox. Un total de catro configuracións deseñáronse para unha planta de 100.000 habitantes equivalentes. Os esquemas baseados na estratexia descrita anteriormente (recuperación de materia orgánica + proceso de nitrificación parcial anammox) comparáronse cun fronte a unha estratexia convencional. Os novos esquemas incorporaron as seguintes tecnoloxías: i) UASB (pola súa abreviatura en inglés, upflow anaerobic sludge blanket) seguido dun proceso de nitrificación parcial-anammox denominado IFAS (pola súa abreviatura en inglés, integrated fixed activated sludge), ii) HRAS (pola RESUMO 23 súa abreviatura en inglés, high rate activated sludge) unido a un IFAS, e finalmente, iii) RBF + CEPT (polas súas abreviaturas en inglés, rotating belt filter; chemical enhanced primary treatment). O esquema convencional foi un clarificador primario acoplado a un sistema convencional de lodos (CAS polas súas siglas en inglés, conventional activated sludge) con eliminación de nitróxeno. Os esquemas propostos mostraron ser máis eficientes en termos de enerxía recuperada a través do biogás. Non obstante, este incremento non xerou unha diminución do perfil ambiental en todas as configuracións, xa que o baseado en RBF + CEPT + IFAS presentou maiores impactos en comparación cos outros sistemas tanto innovadores (UABS + IFAS e HRAS + IFAS) como co convencional (PC + CAS). Este incremento debeuse á adición de químicos que aínda que produza unha mellora no perfil enerxético incrementa os impactos ambientais e económicos. A mellor configuración en termos xerais foi: UASB + IFAS seguido do esquema HRAS + IFAS. O esquema UASB + IFAS presenta a vantaxe de que non precisa dunha liña de lodos moi complexa, xa que a xeración dos lodos é moi baixa nesta configuración. Isto pode axudar a resolver a problemática relacionada coa cantidade de lodos que xeran estes sistemas, así como a súa xestión e posterior aplicación. Outra vantaxe dos sistemas innovadores é que a redución enerxética en aeración cando se incorpora o proceso IFAS pode chegar ata un 13%. Este capítulo serve para comprender que non todos os esquemas innovadores implican mellores resultados. Neste sentido, cando se incorpora unha nova tecnoloxía, non só é necesario unha validación tecnolóxica senón tamén unha validación dende o punto de vista económico e ambiental. Polo tanto, a ferramenta do análise do ciclo de vida permite axudar a valorar estas opcións, o cal pode axudar á hora de tomar decisión ó deseñar unha depuradora. Capítulo 5: Consecuencias ambientais e económicas ligadas á recuperación de enerxía por medio de novos esquemas en plantas de tratamento reais Este capítulo está ligado ó anterior debido a que se busca reducir a xeración de lodo e aumentar a produción enerxética. Propuxéronse RESUMO 24 varios esquemas de tratamento de augas residuais para abordar os desafíos nomeados anteriormente. As modificacións van dende as etapas de modernización, onde se inclúen unidades novidosas en procesos convencionais ata concepcións completamente novas, pasando por modificacións substanciais do diagrama de fluxo. As principais diferenzas con respecto ó capítulo anterior é que agora os esquemas foron implantados en dúas plantas de tratamento reais situadas en distintos países europeos (España e Dinamarca). Para esta avaliación é necesario usar ferramentas para modelar, optimizar e seleccionar a mellor configuración de planta dende un punto de vista técnico, económico e ambiental. En ambas plantas, usáronse datos reais de fluxos de entrada nas depuradoras. Os datos de enerxía, eliminación ou consumo de químicos obtivéronse a partir do modelado, que se fixo co software Matlab, que é un dos máis comúns para modelar plantas de tratamento de augas. Este traballo xurdiu dunha colaboración e estadía na Universidade Técnica de Dinamarca (DTU). Primeiro, modelouse a configuración real de cada planta de tratamento que consisten en un clarificador primario máis un sistema de lodos activos. Unha vez se modelaron esas dúas plantas, o sistema convencional (clarificador primario + sistema de lodos activos) modificouse por dúas opcións alternativas: (i) HRAS + IFAS e (ii) ERBF (pola súa abreviatura en inglés, enhanced rotating belt filter) + IFAS. Os datos obtidos no modelado usáronse para calcular os perfiles ambientais e económicos de cada configuración mencionada anteriormente. As novas configuracións demostraron ser mellores en termos de custos e aforro enerxético, o que propiciou que o perfil ambiental e económico fose menor que nas configuracións convencionais ( PC + CAS). Neste capítulo, o modelado demostrou ser unha ferramenta de cálculo eficiente da cal se poden obter datos válidos para calcular perfís ambientais e económicos para obter unha perspectiva xeral da planta. Neste caso, os novos esquemas axudaron a mellorar o nexo auga-enerxía e conseguir que as plantas de tratamento sexan máis eficientes de maneira integral facendo posible englobar estes sistemas de tratamento dentro da economía circular. RESUMO 25 Capítulo 6: Escalado dunha tecnoloxía innovadora para a análise dos impactos ambientais e económicos Esta primeira sección remata cun capítulo que ten como meta demostrar a escala na cal unha tecnoloxía innovadora proporciona datos e valores fiables para realizar o análise de ciclo de vida e os custos económicos, asegurando o avance na dirección da eco-eficiencia. Así mesmo, a importancia de medir a incerteza das ferramentas de cálculo reside na súa aplicación para sistemas descentralizados (cada vez máis pequenos). Este estudo avaliou os impactos ambientais e económicos dunha tecnoloxía de eliminación de nitróxeno autótrofo (ELAN® polas súas siglas en español, eliminación autótrofa de nitróxeno) dende a concepción de laboratorio (1,5 L) ata a escala real (2 unidades de 115 m3) pasando por dúas unidades a escala piloto (200 L e 1,2 m3). As emisións indirectas relacionadas co consumo de enerxía foron a principal causa de impacto en todas as categorías excepto a eutrofización. Tamén se observou que a medida que a escala incrementa o impacto diminúe. Á hora de avaliar a fiabilidade dos datos, este estudo proporcionou que a mínima á cal ten sentido aplicar a análise de ciclo de vida é de 200 L, mentres que para os indicadores económicos fixouse en 1 m3 de volume de reactor. Polo tanto, se estas ferramentas se aplican a escalas máis pequenas a incerteza dos datos pode condicionar os resultados. A segunda parte da tese doutoral consistiu en estudar os sistemas descentralizados e está formada por dous capítulos (Capítulo 7 e 8) resumidos a continuación. Esta sección está baseada nun proxecto europeo chamado Run4Life (polas súas siglas en inglés, “Recovery and utilization of nutrients 4 low impact fertilizer”). Este proxecto adopta o concepto de economía circular mediante a recuperación enerxética, auga ou biofertilizantes. Con isto o principal obxectivo do proxecto é intentar cambiar o obsoleto concepto fin de liña que se aplica para o tratamento de augas residuais. Para levar a cabo este obxectivo o desenvolvemento tecnolóxico combinarase con factores económicos e ambientais, así como unha avaliación de riscos non só para os compoñentes que poden ser perigosos para a saúde das persoas senón tamén para o medio ambiente. GENERAL INTRODUCTION 32 WWTPs proved to be very effective in removing nitrogen, phosphorus, and organic matter. However, in recent years, emerging pollutants called organic micropollutants (OMPs) have emerged as one of the problems in the WWTPs. OMPs are defined as anthropogenic or natural substances that include personal care products, pesticides, drugs, hormones or pharmaceutical compounds, among others (Barbosa et al., 2016). OMPs can contaminate groundwater, soil or vegetables. WWTPs are not designed to remove these compounds and may promote their dispersion and distribution in the environment (Bellver-Domingo et al., 2017). Beyond the issue of micropollutant removal, WWTPs are characterised by high energy consumption in the process of removing pollutants and generate a significant sludge production that must be managed correctly (Gu et al., 2018). Therefore, these problems can increase the costs of wastewater treatment. In addition, these systems may be considered environmentally and economically unsuitable. Therefore, it is necessary to improve these elements in order to have more sustainable systems. As part of the effort to minimise environmental problems and ensure access to safe water and sanitation systems, the United Nations promoted the adoption of Agenda 2030 for Sustainable Development (United Nations, 2015). In this Agenda, 17 objectives were developed for the protection of people and the planet. With regard to water protection, Goal 6 refers to "clean water and sanitation", which specifies the improvement of water quality, waste minimisation, removal of OMPs and the recovery of wastewater products (United Nations, 2015). So, WWTPs should be adapted to the new demands of the population and must be improved. However, to achieve this purpose, the best way to develop wastewater treatment plants must be sought from an environmental, economic and social point of view, as well as the best treatment strategy to ensure global sanitation and product recovery. The previous answers will be developed in the following sections of Chapter 1 where the change of philosophy of wastewater will be explained through the concept of circular economy (Section 1.2. Circular economy in the wastewater treatment sector). Then, two strategies to CHAPTER 1: INTRODUCTION 33 improve the wastewater treatment sector will be defined and explained (1.3. New wastewater treatment strategy for centralised systems and 1.4. Decentralised approach for the wastewater treatment sections). Then, the environmental strategy (1.5. Life Cycle Assessment methodology and its application to wastewater treatment) and economic strategy (1.6. Economic evaluation) will be explained, and finally the main objectives and motivations for this thesis will be summarised. 1.2. Circular economy in the wastewater treatment sector As mentioned before, in the past, WWTPs have been considered end- of-pipe systems with the main objective of treating a waste and discharging it into the aquatic environment. This end-of-pipe model is known as "linear" economy, which consists of one-directional model in which resources are used to produce goods that are purchased and, finally, the goods are disposed of after a single use (Figure 1.1) (Esposito et al., 2017). Detrimental air environmental quality, long-term economic stability or unsustainability are the main problems of this type of system (Millar et al., 2019). Currently, and in order to try to solve these problems, end-of-pipe systems are being replaced by the approach of circular economy based on a circular flow model. The main objectives are to promote resource recovery, minimise environmental impact and, at the same time, encourage growth (Figure 1.2) (Andersen, 2007). GENERAL INTRODUCTION 34 Figure 1.1. Linear economy philosophy Figure 1.2. Circular economy perception In this framework, the role played by the WWTPs (end-of-pipe elements) should be modified and adapted to this new "circular" philosophy. For this objective, the resource recovery can be a solution. Nutrients (nitrogen and phosphorus) reclaimed water and energy recovery are key factors in meeting this objective. In addition, the reduction of sludge production, as well as energy, have been under the focus for improvement (Leyva-Díaz et al., 2020). These goals can be CHAPTER 1: INTRODUCTION 35 achieved through the modification of the wastewater treatment strategy for centralised systems (section 1.3) or the implementation of decentralised wastewater treatment schemes (section 1.4). To better understand these concepts, both are explained in the following sections. 1.3. New wastewater treatment strategy for centralised systems The conventional approach to wastewater treatment is based on large-scale systems in which wastewater is collected through an extensive sewer network. In general, this implies high construction and operational costs (Massoud et al., 2009). Moreover, the environmental impacts can increase in these wastewater schemes since they are characterised by high energy consumption and large sludge generation (Tang et al., 2020). It is widely known that one of the hotspots in wastewater treatment is the energy consumption in aeration for the biological process (Gikas, 2017). Conventional nitrification-denitrification is based on aerobic and anoxic conditions. In the first stage (nitrification process), ammonium is oxidised to nitrate or nitrite and then both are reduced to dinitrogen gas (denitrification process). Therefore, in nitrification, there is an electricity consumption while in denitrification, organic matter is needed (Iannacone et al., 2019). Energy consumption can vary between 0.3 kWh/m3 to 0.6 kWh/m3 (Wan et al., 2016). Additionally, the C/N ratio should be higher than 5. An insufficient C/N ratio implies the addition of an external OM source which can increase the operational costs and more sludge production (Jiang et al., 2019). Finally, the sludge has a lower methanisation factor because only 30-50% of volatile solids are transformed into methane (Cao and Pawłowski, 2013). So far, much effort has been devoted to exploring new technologies and wastewater alternatives with the main objective of making systems more sustainable and circular (Gu et al., 2018). In this situation, the Anammox process, in which ammonium is directly converted together with nitrite to dinitrogen gas, was a very significant advance in wastewater treatment. In this way, the energy in aeration can be reduced and an external source of OM is not necessary (Vázquez-Padín et al., 2009). Several technologies have been developed to use this pathway to GENERAL INTRODUCTION 36 remove nitrogen. Integrated fixed film activated sludge (IFAS) (Malovanyy et al., 2015a); autotrophic nitrogen removal (ELAN, eliminación autótrofa de nitrógeno, in Spanish) (Morales et al., 2015a) or SHARON-Anammox (Van Dongen et al., 2001) are some of them. However, these technologies do not work properly with a high percentage of solids or a high C/N ratio. Additionally, temperature and pH can be limiting factors (Xu et al., 2015). The problems can be solved with the implementation of a new wastewater strategy that has been maintained in recent years. This approach consists of recovering OM in primary treatment and removing nitrogen with a partial nitrification-Anammox unit. When OM is applied in primary treatment, solids are removed and not incorporated into the secondary treatment. In addition, primary sludge is more biodegradable than secondary sludge, so the methanisation factor is also higher. This implies a greater production of biogas that can be transformed into electricity and heat, making the WWTPs more self-sufficient in terms of energy (Pérez-Elvira and Fernández-Polanco, 2012). New technologies such as rotating belt filters (RBFs), chemically enhanced primary treatment (CEPT) or high rate activated sludge (HRAS) have been included as primary treatments (Gu et al., 2018; Rahman et al., 2019; Ruiken et al., 2013) and others more widespread such as upflow anaerobic sludge blanket (UASB) (Malovanyy et al., 2015b). In addition to this technology substitution and change of strategy in the wastewater line, the sludge line was also improved. As mentioned above, research has been conducted in recent years on how to maximise energy production in wastewater treatment plants to make systems carbon neutral. Today, the environmental and economic advantages of the anaerobic digestion (AD) unit have been proven in great detail (Gianico et al., 2015). However, not all wastewater treatment plants include this type of treatment. AD process consists of four steps: hydrolysis, acidogenesis, acetogenesis and methanogenesis. The first step (hydrolysis) is a limiting step due to polymer and extracellular membrane protections (Dai et al., 2016). On the one hand, the main reason for not implemented the AD at all levels is associated with sludge production. That is, in small wastewater treatment plants, the sludge CHAPTER 1: INTRODUCTION 37 generated is not sufficient to guarantee the use of biogas. To solve this problem, the co-digestion process can be applied in WWTPs. This method is based on the addition of a solid waste rich in organic matter (Gu et al., 2020) and can improve the performance of the AD process to increase biogas production. Alternatively, the integration of a pre-treatment in the sludge line may also favour the process as this type of pre-treatments aim to accelerate the hydrolysis step, and to improve sludge dewatering. Sludge pre-treatments are divided into four main types: thermal, chemical, physical and biological (Abelleira-Pereira et al., 2015; Neumann et al., 2016). Thermal pre-treatment consists of the solubilisation of complex organic matter by increasing temperature and pressure (Serrano et al., 2015). Optimal temperatures can range from 150 °C to 180 °C, while pressure varies from 600-2500 kPa (Elalami et al., 2019). This unit is used to work in cycles of about 30 or 60 min, and depending on the characteristics of the process, can achieve an energy increase of about 51% (Bougrier et al., 2008). Biological processes are based on enzymatic hydrolysis or the addition of fungi/bio-surfactants (Zhen et al., 2017). The addition of these compounds works best at thermophilic temperature because the increase in this variable promotes the hydrolysis of the raw materials (Ge et al., 2010). The increase of methane can fluctuate between 25% and 69% (Bolzonella et al., 2012). Regarding chemical pre-treatments, when there is a chemical addition, alkaline and acidic chemicals are the most studied (Khiewwijit et al., 2015a). However, these alternatives can cause problems of precipitation or inhibition, so their addition must be done very carefully. For this reason, other methods have been studied such as free ammonia (Wei et al., 2018) or oxidation with ozone or H2O2 (Chacana et al., 2017; Yu et al., 2018). The main problems of this type of pretreatment are that ammonia can inhibit the AD process and oxidation requires a lot of energy and a large consumption of chemicals. Thus, these factors can penalize these pre-treatment schemes when introduced into the sludge line. Finally, physical pre-treatment can be divided into high pressure, lysis, microwave and ultrasound. High pressure is similar to thermal pretreatment but only by increasing operating pressure. There are several GENERAL INTRODUCTION 38 publications in which this pre-treatment can achieve a methane enhancement of 60-80% (Engelhart et al., 2000; Khiewwijit et al., 2015b). Lysis is a simple pre-treatment that causes partial cell destruction and improves the biogas field by about 15-26% (Dohányos et al., 1997). As for microwave and ultrasound methods, in addition to improving biogas and sludge dewatering, they can also help eliminate pathogens in the sludge. However, these processes can be energy-intensive, so biogas yield should be higher than in the other scenarios. However, the development of these pre-treatments is still in the laboratory or pilot plant (Feng et al., 2009; Neumann et al., 2016). Although there are a wide range of sludge pre-treatments, they all have the same objectives, namely, to improve biogas production for more independent energy systems and to improve sludge dewatering. In this way, operational costs related to sludge management can be significantly reduced. Therefore, the new design of the WWTP can include all these concepts. However, it is true that many of these technologies are still under development and more research is needed to ensure that these assumptions are fulfilled. 1.4. Decentralised approach for wastewater treatment As mentioned above, wastewater treatment is constantly changing to seek different approaches that are more sustainable. Within this framework, the decentralised system of wastewater treatment has gained strength in recent years (Hophmayer-Tokich, 2006). These systems are based on the separation of wastewater generated at different points in a household. Black water (BW) is generated in toilets, while grey water (GW) refers to water from laundry, showers, sinks or dishwashers (Ashok et al., 2018). Finally, kitchen waste (KW) is organic waste and can be treated with the BW or separately. The main advantages of these systems compared to the centralised perspective are flexibility and the elimination of long sewer systems (Leigh and Lee, 2019). In addition, water reuse and nutrient recovery are increased due to source separation. While BW and KW are more appropriate for energy and nutrient recovery, GW is used in irrigation because the concentration of pollutants is very low (Kobayashi et al., CHAPTER 1: INTRODUCTION 39 2020). These systems are also more appropriate for rural areas and developing countries because investment and maintenance costs can be economically more viable than conventional systems (Machado et al., 2017; Zeng et al., 2017). Decentralised systems combine technologies that are applied in conventional wastewater treatment plants and more innovative ones. Regarding GW, several technologies have been studied in recent years (Ashok et al., 2018; Boyjoo et al., 2013). The most applicable are constructed wetlands (CW) due to the simplicity of operation and low energy consumption that implies lower operating costs (Garfí et al., 2017; Wu et al., 2015). In simple terms, this technology is considered as a complex natural bioreactor in which iterations occur between plants, soil and sediments (Corroto et al., 2019). The type of vegetation, substrate, microorganism and physicochemical parameters are key factors for its application (Corroto et al., 2019; Hijosa-Valsero et al., 2011). However, these systems require a large land area, which can be troublesome for their implementation (Arden and Ma, 2018). In this context, membrane bioreactors (MBRs), moving bed biofilm bioreactors (MBBRs) and sequencing batch reactors (SBRs) have emerged as an alternative for treating GW. These systems are more compact, so the land use is lower than in GW and provide a high-quality effluent. However, these technologies are more operationally complex and electricity consumption is higher than in CWs (Cecconet et al., 2019; Jabri et al., 2020). The operation of these units consists of a combination of aeration and non-aeration periods. The main difference is that in MBR and MBBR there is a membrane integrated in the unit (Komesli and Gökçay, 2014), while in SBR the removal of OM or nutrients is accomplished (Vázquez-Padín et al., 2010a). The effluent can be used for irrigation of green areas, street washing or filling toilets (Chen and Wang, 2009) (Figure 1.3). GENERAL INTRODUCTION 40 Figure 1.3. Most commonly used technologies for the treatment of greywater. Abbreviations: GW: grey water, CWs: constructed wetlands, SBR: sequencing batch reactors and MBR: membrane bioreactors. BW and KW can be treated together or separately, but the goal is the same (nutrients and energy recovery). In terms of BW, it is important to distinguish the type of toilets that can be implemented in a house. Conventional toilets are the most common and vacuum toilets (new systems). In conventional toilets, water consumption is high, between 6- 8 L per flush, while in vacuum toilets it is approximately 1-2 L per flush (Gao et al., 2019). This implies that in vacuum toilets wastewater is more concentrated and the production of biogas will be higher than in conventional toilets. However, vacuum toilets entail energy consumption and the noise generated by each flush can be very annoying (Bisschops et al., 2019). The main technologies used to treat this type of wastewater are UASB (Kujawa-Roeleveld et al., 2006) and anaerobic membrane bioreactors (anMBR) (Pretel et al., 2016). Both are characterised by the transformation of OM into biogas, which is valorised into electricity and heat. In addition, high temperature anaerobic digestion (HTAD) has been developed in recent years to treat BW. The main difference with the other technologies is that this reactor works at temperatures of about 70 °C. This means that the water is free of pathogens and can be applied directly CHAPTER 1: INTRODUCTION 41 to agricultural irrigation (Zhang et al., 2020). AnMBRs and UASB can work at ambient or mesophilic temperature (about 35 °C). However, when these units work at ambient temperature, they may have problems with dissolved methane in the effluent, so this factor should be taken into account when applying them (Allegue et al., 2020). In addition to energy, nutrient recovery is carried out in this type of wastewater (BW and KW). Within this framework, the struvite unit is the most studied method of phosphorus recovery and consists of a physicalchemical separation in which magnesium salts are added to facilitate struvite precipitation (Ishii and Boyer, 2015). In this unit, the pH is a key parameter and must be controlled in a range between 8-9 (Liu et al., 2008). In addition, many different types of reactors have been studied by different authors to achieve the best phosphorus recovery (Le Corre et al., 2009; Rahaman et al., 2014). Other technologies focus on nitrogen recovery, such as stripping methods or bioelectrochemical systems (BES). Stripping methods and subsequent sorption in sulphuric or nitrous acid are highly energydependent (Bisschops et al., 2019). Bioelectrochemical processes could separate different types of ions such as NO3-, NO2- or NH4+ (Kuntke et al., 2018). The total ammonia nitrogen is concentrated by the influence of an electrical current and transported to the cathode. Nitrogen is then recovered through stripping. However, in this method, there is no chemical addition (Bisschops et al., 2019). The main technologies for treating BW and KW are summarised in Figure 1.4. GENERAL INTRODUCTION 48 (2018) analysed tertiary technologies and sludge management alternatives or different nitrogen removal technologies (Jafarinejad, 2017). Moreover, other authors studied the total costs of a given technology. Pretel et al., (2016) estimated that an anMBR unit can be values between 0.03 to 0.12 €/m3. In the case of MBR technology, there are more studies that estimated higher values of 0.08 to 0.25 €/m3 (Gil et al., 2010). More recently, for decentralised technologies, Resende et al. (2019) studied wetland costs, between 1.55 $/m3 to 0.84 $/m3. However, it is important to note that the economic indicators can change considerably from country to country and over the years. These changes are related to changes in electricity, personnel or chemicals, among others. In this thesis, the costs will be adapted to the different configurations and countries and will be calculated taking into account the possible deviations. 1.7. Thesis outline: objectives and structure The main goal of this doctoral thesis was to analyse and compare different wastewater treatment configurations from an environmental and economic point of view to provide insights on the sustainability of existing and innovative schemes of wastewater treatment. With this in mind, the thesis was structured in 2 sections: one for centralised systems and other for decentralised schemes. Section I is developed in 5 chapters, whereas Section II is composed by 2 chapters. Finally, the main conclusions of this thesis will be summarised in Chapter 9. Chapter 1 presents the state of the art in the wastewater treatment sector. The main objective is to have a general idea about the problems of the wastewater sector, the importance of the circular economy and the different schemes that can be implemented to improve WWTPs. Moreover, the methodological tools used in this thesis will be explained to better understand its application. Section I: Improving centralised wastewater systems. In this section different schemes and technologies were evaluated to improve the energy-water nexus from an environmental and economic point of view. Chapters 2 and 3 are focused on technologies for improving the sludge line at different sizes. In Chapters 4 and 5, wastewater treatment CHAPTER 1: INTRODUCTION 49 schemes will be changed. New configurations will be explored from an environmental and economic point of view to try to search more efficient configurations. In Chapter 5, two real WWTPs in different countries will be analysed and compared with the existing plant. The main objective of this work is to achieve more efficient systems that do not depend on the electricity grid, as well as to improve the quality of the effluents. Finally, the last chapter that takes part in this section (Chapter 6) has as objective to assess the scale-up of a technology focused on nutrient removal. The main reason for evaluating this technology is to verify the reliability of the LCA and economic indicators in small scale as, for example, in decentralised systems. In this way, these results can serve to have a reference when the decentralised systems (section II) are studied. Section II: Changing the paradigm of wastewater treatment. This section is focused on the evaluation and implementation of different decentralised configurations. In Chapter 7, a wastewater treatment plant based on a MBR is going to analyse for recovering reclaimed water in Turkey which is a country with water deficit. Additionally, the construction phase will be included in the analysis to know how affect the construction in the decentralised wastewater schemes. In Chapter 8, two decentralised schemes are studied at neighbourhood level and compared with a centralised system with the main objective to know if the carbon footprint and water consumption of a person who lives in a decentralised area increase or decrease in comparison with a person that decide to live in a centralised zone. In this case, the chapters cover the concept of recovery (energy and water) but also from the inhabitant perspective. Conclusions. The conclusions chapter aims to give a holistic and integrated view of the main findings and justifies the main contributions of the study. First, a comparison between different centralized schemes will be evaluated to show which is the best configuration in terms of energy, effluent quality and sludge production. Finally, in the decentralized schemes, the main findings and advantages of these systems in terms of energy and water recovery will be summarized. GENERAL INTRODUCTION 50 1.8. References Abelleira-Pereira, J.M., Pérez-Elvira, S.I., Sánchez-Oneto, J., de la Cruz, R., Portela, J.R., Nebot, E., 2015. Enhancement of methane production in mesophilic anaerobic digestion of secondary sewage sludge by advanced thermal hydrolysis pretreatment. Water Res. 71, 330–340. https://doi.org/ 10.1016/j.watres.2014.12.027 Allegue, T., Carballo-Costa, M.N., Fernandez-Gonzalez, N., Garrido, J.M., 2020. Simultaneous nitrogen and dissolved methane removal from an upflow anaerobic sludge blanket reactor effluent using an integrated fixed-film activated sludge system. J. Environ. Manage. 263, 110395. https://doi.org/10.1016/j.jenvman.2020.110395 Álvarez, M.D., Buscio, V., López-Grimau, V., Gutiérrez-Bouzán, C., 2020. LCA study of a new electrochemical and ultraviolet (EC-UV) combined system to decolourise and reuse textile saline effluents: Environmental evaluation and proposal to improve the production process. Chem. Eng. J. 392, 123696. https://doi.org/10.1016/j.cej.2019.123696 Andersen, M.S., 2007. An introductory note on the environmental economics of the circular economy. Sustain. Sci. 2, 133–140. https://doi.org/10.1007/ s11625-006-0013-6 Arden, S., Ma, X., 2018. Constructed wetlands for greywater recycle and reuse: A review. Sci. Total Environ. 630, 587–599. https://doi.org/10.1016/ j.scitotenv.2018.02.218 Arzate, S., Pfister, S., Oberschelp, C., Sánchez-Pérez, J.A., 2019. Environmental impacts of an advanced oxidation process as tertiary treatment in a wastewater treatment plant. Sci. Total Environ. 694. https://doi.org/ 10.1016/j.scitotenv.2019.07.378 Ashok, S.S., Kumar, T., Bhalla, K., 2018. Integrated Greywater Management Systems: A Design Proposal for Efficient and Decentralised Greywater Sewage Treatment. Procedia CIRP 69, 609–614. https://doi.org/10.1016/ j.procir.2017.11.098 Barbosa, M.O., Moreira, N.F.F., Ribeiro, A.R., Pereira, M.F.R., Silva, A.M.T., 2016. Occurrence and removal of organic micropollutants: An overview of the watch list of EU Decision 2015/495. Water Res. 94, 257–279. https://doi.org/10.1016/j.watres.2016.02.047 CHAPTER 1: INTRODUCTION 51 Bellver-Domingo, A., Fuentes, R., Hernández-Sancho, F., 2017. Shadow prices of emerging pollutants in wastewater treatment plants: Quantification of environmental externalities. J. Environ. Manage. 203, 439–447. https://doi.org/10.1016/j.jenvman.2017.08.025 Bisschops, I., Kjerstadius, H., Meulman, B., van Eekert, M., 2019. Integrated nutrient recovery from source-separated domestic wastewaters for application as fertilisers. Curr. Opin. Environ. Sustain. 40, 7–13. https://doi.org/10.1016/j.cosust.2019.06.010 Bolzonella, D., Cavinato, C., Fatone, F., Pavan, P., Cecchi, F., 2012. High rate mesophilic, thermophilic, and temperature phased anaerobic digestion of waste activated sludge: A pilot scale study. Waste Manag. 32, 1196–1201. https://doi.org/10.1016/j.wasman.2012.01.006 Bougrier, C., Delgenès, J.P., Carrère, H., 2008. Effects of thermal treatments on five different waste activated sludge samples solubilisation, physical properties and anaerobic digestion. Chem. Eng. J. 139, 236–244. https://doi.org/ 10.1016/j.cej.2007.07.099 Boyjoo, Y., Pareek, V.K., Ang, M., 2013. A review of greywater characteristics and treatment processes. Water Sci. Technol. 67, 1403–1424. https://doi.org/ 10.2166/wst.2013.675 Cao, Y., Pawłowski, A., 2013. Life cycle assessment of two emerging sewage sludge-to-energy systems: Evaluating energy and greenhouse gas emissions implications. Bioresour. Technol. 127, 81–91. https://doi.org/ 10.1016/j.biortech.2012.09.135 Carr, G., Potter, R.B., Nortcliff, S., 2011. Water reuse for irrigation in Jordan: Perceptions of water quality among farmers. Agric. Water Manag. 98, 847– 854. https://doi.org/10.1016/j.agwat.2010.12.011 Cecconet, D., Callegari, A., Hlavínek, P., Capodaglio, A.G., 2019. Membrane bioreactors for sustainable, fit-for-purpose greywater treatment: a critical review. Clean Technol. Environ. Policy 21, 745–762. https://doi.org/ 10.1007/s10098-019-01679-z Chacana, J., Alizadeh, S., Labelle, M.A., Laporte, A., Hawari, J., Barbeau, B., Comeau, Y., 2017. Effect of ozonation on anaerobic digestion sludge activity and viability. Chemosphere 176, 405–411. https://doi.org/10.1016/ j.chemosphere.2017.02.108 GENERAL INTRODUCTION 52 Chen, R., Wang, X.C., 2009. Cost-benefit evaluation of a decentralized water system for wastewater reuse and environmental protection. Water Sci. Technol. 59, 1515–1522. https://doi.org/10.2166/wst.2009.156 Corominas, L., Foley, J., Guest, J.S., Hospido, A., Larsen, H.F., Morera, S., Shaw, A., 2013. Life cycle assessment applied to wastewater treatment: State of the art. Water Res. 47, 5480–5492. https://doi.org/10.1016/ j.watres.2013. 06.049 Corroto, C., Iriel, A., Cirelli, A.F., Carrera, A.L.P., 2019. Science of the Total Environment Constructed wetlands as an alternative for arsenic removal from reverse osmosis effluent. Sci. Total Environ. 691, 1242–1250. https://doi.org/10.1016/j.scitotenv.2019.07.234 Dai, X., Li, X., Zhang, D., Chen, Y., Dai, L., 2016. Simultaneous enhancement of methane production and methane content in biogas from waste activated sludge and perennial ryegrass anaerobic co-digestion: The effects of pH and C/N ratio. Bioresour. Technol. 216, 323–330. https://doi.org/ 10.1016/j.biortech.2016.05.100 De Bruyn, S., Bijleveld, M., de Graaff, L., Schep, E., Schroten, A., Vergeer, R., Ahdour, S., 2018. Environmental Prices Handbook EU28 Version. CE Delft 175. Dohányos, M., Zábranská, J., Jenícek, P., 1997. Enhancement of sludge anaerobic digestion by use of a special thickening centrifuge. Water Sci. Technol. 36, 145–153. https://doi.org/10.1016/S0273-1223(97)00677-X Elalami, D., Carrere, H., Monlau, F., Abdelouahdi, K., Oukarroum, A., Barakat, A., 2019. Pretreatment and co-digestion of wastewater sludge for biogas production: Recent research advances and trends. Renew. Sustain. Energy Rev. 114, 109287. https://doi.org/10.1016/j.rser.2019.109287 Engelhart, M., Krüger, M., Kopp, J., Dichtl, N., 2000. Effects of disintegration on anaerobic degradation of sewage excess sludge in downflow stationary fixed film digesters. Water Sci. Technol. 41, 171–179. https://doi.org/ 10.2166/wst.2000.0069 Esposito, M., Tse, T., Soufani, K., 2017. Is the Circular Economy a New Fast- Expanding Market? Thunderbird Int. Bus. Rev. 59, 9–14. https://doi.org/10.1002/tie.21764 CHAPTER 1: INTRODUCTION 53 Feng, X., Deng, J., Lei, H., Bai, T., Fan, Q., Li, Z., 2009. Dewaterability of waste activated sludge with ultrasound conditioning. Bioresour. Technol. 100, 1074–1081. https://doi.org/10.1016/ j.biortech.2008.07.055 Foley, J., de Haas, D., Hartley, K., Lant, P., 2010. Comprehensive life cycle inventories of alternative wastewater treatment systems. Water Res. 44, 1654–1666. https://doi.org/10.1016/ j.watres.2009.11.031 Gallego, A., Hospido, A., Moreira, M.T., Feijoo, G., 2008. Environmental performance of wastewater treatment plants for small populations. Resour. Conserv. Recycl. 52, 931–940. https://doi.org/10.1016/ j.resconrec.2008.02.001 Gao, M., Guo, B., Zhang, L., Zhang, Y., Liu, Y., 2019. Microbial community dynamics in anaerobic digesters treating conventional and vacuum toilet flushed blackwater. Water Res. 160, 249–258. https://doi.org/10.1016/ j. watres.2019.05.077 Garfí, M., Flores, L., Ferrer, I., 2017. Life Cycle Assessment of wastewater treatment systems for small communities: Activated sludge, constructed wetlands and high rate algal ponds. J. Clean. Prod. 161, 211–219. https://doi.org/10.1016/j.jclepro.2017.05.116 Ge, H., Jensen, P.D., Batstone, D.J., 2010. Pre-treatment mechanisms during thermophilic-mesophilic temperature phased anaerobic digestion of primary sludge. Water Res. 44, 123–130. https://doi.org/10.1016/ j. watres.2009.09.005 Gianico, A., Bertanza, G., Braguglia, C.M., Canato, M., Laera, G., Heimersson, S., Svanström, M., Mininni, G., 2015. Upgrading a wastewater treatment plant with thermophilic digestion of thermally pre-treated secondary sludge: Techno-economic and environmental assessment. J. Clean. Prod. 102, 353– 361. https://doi.org/10.1016/j.jclepro.2015.04.051 Gikas, P., 2017. Towards energy positive wastewater treatment plants. J. Environ. Manage. 203, 621–629. https://doi.org/10.1016/j.jenvman.2016.05.061 Gil, J.A., Túa, L., Rueda, A., Montaño, B., Rodríguez, M., Prats, D., 2010. Monitoring and analysis of the energy cost of an MBR. Desalination 250, 997–1001. https://doi.org/10.1016/ j.desal.2009.09.089 GENERAL INTRODUCTION 54 Gu, J., Liu, R., Cheng, Y., Stanisavljevic, N., Li, L., Djatkov, D., Peng, X., Wang, X., 2020. Anaerobic co-digestion of food waste and sewage sludge under mesophilic and thermophilic conditions: Focusing on synergistic effects on methane production. Bioresour. Technol. 301, 122765. https://doi.org/ 10.1016/j.biortech.2020.122765 Gu, J., Yang, Q., Liu, Y., 2018. Mainstream anammox in a novel A-2B process for energy-efficient municipal wastewater treatment with minimized sludge production. Water Res. 138, 1–6. https://doi.org/10.1016/ j.watres.2018.02.051 Harclerode, M., Doody, A., Brower, A., Vila, P., Ho, J., Evans, P.J., 2020. Life cycle assessment and economic analysis of anaerobic membrane bioreactor whole-plant configurations for resource recovery from domestic wastewater. J. Environ. Manage. 269, 110720. https://doi.org/10.1016/ j.jenvman.2020.110720 Hauck, M., Maalcke-Luesken, F.A., Jetten, M.S.M., Huijbregts, M.A.J., 2016. Removing nitrogen from wastewater with side stream anammox: What are the trade-offs between environmental impacts? Resour. Conserv. Recycl. 107, 212–219. https://doi.org/10.1016/ j.resconrec.2015.11.019 Hijosa-Valsero, M., Sidrach-Cardona, R., Martín-Villacorta, J., Cruz Valsero- Blanco, M., Bayona, J.M., Bécares, E., 2011. Statistical modelling of organic matter and emerging pollutants removal in constructed wetlands. Bioresour. Technol. 102, 4981–4988. https://doi.org/10.1016/ j.biortech.2011.01.063 Hophmayer-Tokich, S., 2006. Wastewater Management Strategy: centralized versus decentralized technologies for small communities. CSTM-reeks 271, 27. Iannacone, F., Di Capua, F., Granata, F., Gargano, R., Pirozzi, F., Esposito, G., 2019. Effect of carbon-to-nitrogen ratio on simultaneous nitrification denitrification and phosphorus removal in a microaerobic moving bed biofilm reactor. J. Environ. Manage. 250, 109518. https://doi.org/10.1016/ j.jenvman.2019.109518 Ioannou-Ttofa, L., Foteinis, S., Chatzisymeon, E., Michael-Kordatou, I., Fatta- Kassinos, D., 2017. Life cycle assessment of solar-driven oxidation as a polishing step of secondary-treated urban effluents. J. Chem. Technol. Biotechnol. 92, 1315–1327. https://doi.org/10.1002/jctb.5126 CHAPTER 1: INTRODUCTION 55 Ishii, S.K.L., Boyer, T.H., 2015. Life cycle comparison of centralized wastewater treatment and urine source separation with struvite precipitation: Focus on urine nutrient management. Water Res. 79, 88–103. https://doi.org/10.1016/j.watres.2015.04.010 ISO 14040, 2006. International Organization for Standardization, ISO 14040. Environmental Management-Life Cycle Assessment - Principles and Framework, Geneve. Jafarinejad, S., 2017. Cost estimation and economical evaluation of three configurations of activated sludge process for a wastewater treatment plant (WWTP) using simulation. Appl. Water Sci. 7, 2513–2521. https://doi.org/10.1007/s13201-016-0446-8 Jiang, C., Xu, S., Wang, R., Feng, S., Zhou, S., Wu, Shimin, Zeng, X., Wu, Shanghua, Bai, Z., Zhuang, G., Zhuang, X., 2019. Achieving efficient nitrogen removal from real sewage via nitrite pathway in a continuous nitrogen removal process by combining free nitrous acid sludge treatment and DO control. Water Res. 161, 590–600. https://doi.org/10.1016/j.watres.2019.06.040 Jiang, Y., 2009. China’s water scarcity. J. Environ. Manage. 90, 3185–3196. https://doi.org/10.1016/ j.jenvman.2009.04.016 Kalbar, P.P., Karmakar, S., Asolekar, S.R., 2013. Assessment of wastewater treatment technologies : life cycle approach 27, 261–268. https://doi.org/10.1111/wej.12006 Kehrein, P., Van Loosdrecht, M., Osseweijer, P., Garfí, M., Dewulf, J., Posada, J., 2020. A critical review of resource recovery from municipal wastewater treatment plants-market supply potentials, technologies and bottlenecks. Environ. Sci. Water Res. Technol. 6, 877–910. https://doi.org/10.1039/ c9ew00905a Khalil, N., Sinha, R., Raghava, a K., Mittal, a K., 2008. UASB Technology for Sewage Treatment in India: Experience, Economic Evaluation and its Potential in Other Developing Countries. Twelfth Int. Water Technol. Conf. 1411–1427. Khiewwijit, R., Temmink, H., Labanda, A., Rijnaarts, H., Keesman, K.J., 2015a. Production of volatile fatty acids from sewage organic matter by combined bioflocculation and alkaline fermentation. Bioresour. Technol. 197, 295– 301. https://doi.org/10.1016/j.biortech.2015.08.112 GENERAL INTRODUCTION 56 Khiewwijit, R., Temmink, H., Rijnaarts, H., Keesman, K.J., 2015b. Energy and nutrient recovery for municipal wastewater treatment: How to design a feasible plant layout? Environ. Model. Softw. 68, 156–165. https://doi.org/10.1016/j.envsoft.2015.02.011 Kobayashi, Y., Ashbolt, N.J., Davies, E.G.R., Liu, Y., 2020. Life cycle assessment of decentralized greywater treatment systems with reuse at different scales in cold regions. Environ. Int. 134, 105215. https://doi.org/10.1016/ j.envint.2019.105215 Kobetičová, K., Černý, R., 2019. Terrestrial eutrophication of building materials and buildings: An emerging topic in environmental studies. Sci. Total Environ. 689, 1316–1328. https://doi.org/10.1016/ j.scitotenv.2019. 06.423 Komesli, O.T., Gökçay, C.F., 2014. Investigation of sludge viscosity and its effects on the performance of a vacuum rotation membrane bioreactor. Environ. Technol. (United Kingdom) 35, 645–652. https://doi.org/10.1080/ 09593330.2013.840655 Kujawa-Roeleveld, K., Elmitwalli, T., Zeeman, G., 2006. Enhanced primary treatment of concentrated black water and kitchen residues within DESAR concept using two types of anaerobic digesters. Water Sci. Technol. 53, 159–168. https://doi.org/10.2166/wst.2006.265 Kumar, B., Bhardwaj, N., Agrawal, K., Chaturvedi, V., Verma, P., 2020. Current perspective on pretreatment technologies using lignocellulosic biomass: An emerging biorefinery concept. Fuel Process. Technol. 199. https://doi.org/10.1016/j.fuproc.2019.106244 Kuntke, P., Sleutels, T.H.J.A., Rodríguez Arredondo, M., Georg, S., Barbosa, S.G., ter Heijne, A., Hamelers, H.V.M., Buisman, C.J.N., 2018. (Bio)electrochemical ammonia recovery: progress and perspectives. Appl. Microbiol. Biotechnol. 102, 3865–3878. https://doi.org/10.1007/s00253-018-8888-6 Le Corre, K.S., Valsami-Jones, E., Hobbs, P., Parsons, S.A., 2009. Phosphorus recovery from wastewater by struvite crystallization: A review, Critical Reviews in Environmental Science and Technology. https://doi.org/ 10.1080/10643380701640573 Leigh, N.G., Lee, H., 2019. Sustainable and resilient urban water systems: The role of decentralization and planning. Sustain. 11. https://doi.org/10.3390/ su11030918 CHAPTER 1: INTRODUCTION 57 Leyva-Díaz, J.C., Monteoliva-García, A., Martín-Pascual, J., Munio, M.M., García- Mesa, J.J., Poyatos, J.M., 2020. Moving bed biofilm reactor as an alternative wastewater treatment process for nutrient removal and recovery in the circular economy model. Bioresour. Technol. 299, 122631. https://doi.org/10.1016/j.biortech.2019.122631 Li, W., Li, L., Qiu, G., 2017. Energy consumption and economic cost of typical wastewater treatment systems in Shenzhen, China. J. Clean. Prod. 163, S374–S378. https://doi.org/10.1016/ j.jclepro.2015.12.109 Li, Y., Zhang, S., Zhang, W., Xiong, W., Ye, Q., Hou, X., Wang, C., Wang, P., 2019. Life cycle assessment of advanced wastewater treatment processes: Involving 126 pharmaceuticals and personal care products in life cycle inventory. J. Environ. Manage. 238, 442–450. https://doi.org/10.1016/ j.jenvman.2019.01.118 Lijó, L., Malamis, S., González-García, S., Moreira, M.T., Fatone, F., Katsou, E., 2017. Decentralised schemes for integrated management of wastewater and domestic organic waste: the case of a small community. J. Environ. Manage. 203, 732–740. https://doi.org/10.1016/ j.jenvman.2016.11.053 Liu, Z., Zhao, Q., Wang, K., Lee, D., Qiu, W., Wang, J., 2008. Urea hydrolysis and recovery of nitrogen and phosphorous as MAP from stale human urine. J. Environ. Sci. 20, 1018–1024. https://doi.org/10.1016/S1001- 0742(08)62202-0 Longo, S., Frison, N., Renzi, D., Fatone, F., Hospido, A., 2017. Is SCENA a good approach for side-stream integrated treatment from an environmental and economic point of view? Water Res. 125, 478–489. https://doi.org/10.1016/j.watres.2017.09.006 Lorenzo-Toja, Y., Alfonsín, C., Amores, M.J., Aldea, X., Marin, D., Moreira, M.T., Feijoo, G., 2016a. Beyond the conventional life cycle inventory in wastewater treatment plants. Sci. Total Environ. 553, 71–82. https://doi.org/10.1016/j.scitotenv.2016.02.073 Lorenzo-Toja, Y., Vázquez-Rowe, I., Amores, M.J., Termes-Rifé, M., Marín- Navarro, D., Moreira, M.T., Feijoo, G., 2016b. Benchmarking wastewater treatment plants under an eco-efficiency perspective. Sci. Total Environ. 566–567, 468–479. https://doi.org/10.1016/ j.scitotenv.2016.05.110 GENERAL INTRODUCTION 64 Zepon, T., Ricardo, R., Azapagic, A., 2018. Life cycle environmental impacts of advanced wastewater treatment techniques for removal of pharmaceuticals and personal care products (PPCPs). J. Environ. Manage. 215, 258–272. https://doi.org/10.1016/j.jenvman.2018.03.047 Zessner, M., Lampert, C., Kroiss, H., Lindtner, S., 2010. Cost comparison of wastewater treatment in Danubian countries. Water Sci. Technol. 62, 223– 230. https://doi.org/10.2166/wst.2010.271 Zhang, Q., Zhang, L., Guo, B., Liu, Y., 2020. Mesophiles outperform thermophiles in the anaerobic digestion of blackwater with kitchen residuals: Insights into process limitations. Waste Manag. 105, 279–288. https://doi.org/10.1016/j.wasman.2020.02.018 Zhu, L., Liu, B., Wang, F., Bi, J., 2013. Raising discharge standards leads to environmental problem shifting in China. Water Sci. Technol. 68, 2605– 2612. https://doi.org/10.2166/wst.2013.537 IMPROVING CENTRALISED WASTEWATER TREATMENT SYSTEMS Andrea Arias*a, Gumersindo Feijooa, María Teresa Moreiraa. “What is the best scale for implementing the anaerobic digestion according to environmental and economic indicators?” Journal of Water Process and Engineering. 2020, Vol. 32, 101235. https://doi.org/10.1016/j.jwpe.2020.101235. aCRETUS institute. Department of Chemical Engineering. Universidade de Santiago de Compostela, E-15782, Santiago de Compostela, Galicia, Spain CHAPTER 2: Identifying environmental and economic barriers associated with the scale of operation in the anaerobic digestion process SUMMARY WWTPs are the most widely used environmental management systems to ensure that water pollution is properly managed. Since energy costs are the largest factor in operating costs, new installations are designed under energy optimisation parameters. The AD unit allows the valorisation of the organic load into bioenergy. However, not all WWTPs incorporate this technology in the sludge line since a minimum scale plant is required to guarantee stable and profitable operation of the unit. Small treatment plants imply a certain oversizing of electromechanical equipment, so that the unit consumption in such plants is relatively high. In large treatment plants, the design and sizing are optimized to achieve greater control over energy consumption. With the decentralized context gaining momentum, it is important to assess the viability of AD in small plants. In this chapter, four different sludge lines with different plant sizes were evaluated from an environmental and economic point of view. The sludge lines range from 25,000 to 1,000,000 of equivalent inhabitants, although the small sludge line has no AD unit. A gate-to-gate approach was selected to perform the LCA. According to the results obtained in Chapter 2, the environmental impacts of the AD technology are not correlated with the size of the plant, so that not only medium and largescale plants report environmental and economic benefits, but also smaller ones, provided that the premise of biogas flow valorisation into bioenergy is met. Moreover, the AD technology can be improved with the addition of agrowaste that can enhance the organic load in anaerobic digestor and improve the yield of biogas production and the ecoefficiency. This alternative allows to improve the technological, economic and environmental viability of the process. SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 68 TABLE OF CONTENTS-CHAPTER 2 2.1. Introduction ............................................................................................... 69 2.2. Materials and methods ........................................................................... 70 2.2.1. Goal and scope definition .............................................................. 70 2.2.2. Functional unit .................................................................................. 71 2.2.3. System boundaries .......................................................................... 71 2.2.4. Life cycle inventory approach ..................................................... 73 2.2.5. Life cycle impact assessment and interpretation ................. 76 2.2.6. Economic indicators ........................................................................ 77 2.3. Results and discussion ........................................................................... 77 2.3.1. Environmental profile of the different sludge lines ............ 77 2.3.2. Assessment of the feasibility of the anaerobic digestion (AD) unit .......................................................................................................... 80 2.3.3. Energy benefit in the different sludge lines ........................... 82 2.3.4. Economic analysis of the different sludge lines .................... 83 2.4. Conclusions ................................................................................................ 85 2.5. References .................................................................................................. 85 CHAPTER 2: IDENTIFYING ENVIRONMENTAL AND ECONOMIC BARRIERS ASSOCIATED WITH THE SCALE OF OPERATION IN THE ANAEROBIC DIGESTION PROCESS 69 2.1. INTRODUCTION As mentioned in Chapter 1, the WWTPs are essential actors for the treatment of wastewater prior to its discharge into the environment (Pan et al., 2015). In this context, the configuration of new facilities is undergoing a process of dynamic change through the implementation of technologies that entail lower environmental impacts and economic costs (Gude, 2015). In general, the high costs related to sludge management and low energy production are two key factors that penalise the operation of WWTPs. In terms of operational costs, sludge production can imply about 50% of the total costs in a WWTP (Lorenzo-Toja et al., 2016b). Among the different technologies of sludge treatment, the most widely implemented alternative is constituted by a thickening unit followed by homogenisation and dewatering units (Rodriguez-Garcia et al., 2011). In this scheme, sludge is treated as a waste, so there are no environmental or economic benefits. The most widely used alternative in WWTPs for the valorisation of biogas is the AD process. Moreover, the solid fraction can be used as fertiliser (Karagiannidis and Perkoulidis, 2009). However, not all WWTPs integrate this sludge treatment scheme, which is attributed to the need for a minimum size of the treatment plant to ensure stable and cost-effective operation of the unit. In the context of population growth, in which new treatment plants are planned to treat the wastewater of newly built dwellings with limited centralised services, there is an undeniable interest in assessing the viability of the AD technology at different sizes. In this framework, it is interesting to combine an environmental approach with the economic or costs analysis associated with wastewater and sludge treatments (Nelson et al., 2008). Bearing in mind that this unit has significant benefits, the question arises as to why it is not a universal and undeniable option for any type of treatment plant. In addition, it is important to compare sludge lines lacking an AD unit with schemes that incorporate this technology in order to validate or rule out its implementation. With this in mind, the main goal of Chapter 2 was to evaluate the implementation of the AD unit not only on a technological basis, but also on the economic and environmental advantages that this SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 70 unit may have in different plant sizes. Consequently, it is important to define the scale of the treatment plant from which it is convenient to set up the AD technology according to environmental and economic criteria and to identify the existing barriers that impede a generalised implementation. 2.2. MATERIALS AND METHODS 2.2.1. Goal and scope definition Environmental and economic indicators of the different sludge lines of real WWTPs, all of them located in Spain, were evaluated. Four plant sizes were selected: i) one small (Scenario 0: 25,000 equivalent inhabitants); ii) two medium (Scenarios 1 and 2: 200,000 and 400,000 equivalent inhabitants, respectively) and, finally, iii) one large (Scenario 3: 1,000,000 equivalent inhabitants). The plants have different wastewater treatment flows, from 6,250 m3/d for S0 to 213,410 m3/d for S3. The plants are mainly based on the activated sludge process to remove OM. The small plant does not have a primary treatment, but only a pre-treatment to remove greases and solids, while the medium and large plants have a primary treatment to remove solids and OM. For all scenarios, a composting unit for the sludge was considered as a management option as a biofertiliser. The main differences correspond to the sludge line scheme. The small plant (S0) consists of a thickening unit, a homogeniser and, finally, a filtration unit with a dewatering band filter. It is therefore a basic sludge line without an AD unit. The other plants have an analogous configuration, except for the fact that they include an AD unit of different size, coupled to a cogeneration heat power (CHP) unit to transform biogas into electricity (Figure 2.1). CHAPTER 2: IDENTIFYING ENVIRONMENTAL AND ECONOMIC BARRIERS ASSOCIATED WITH THE SCALE OF OPERATION IN THE ANAEROBIC DIGESTION PROCESS 71 Figure 2.1. Different WWTP localisation considered in this study 2.2.2. Functional unit In this case, the study is focused on biogas production, but it is not possible to choose 1 kWh of energy produced because the small plant does not have an AD unit, which would not allow the comparison of different types of plant. For this reason, 1 ton of mixed sludge was selected as FU, according to other publications related to the topic of sludge management (Dong et al., 2014). 2.2.3. System boundaries To make the environmental assessment of the different sludge lines, only the impacts associated to the operational phase were taken into account. The environmental impacts related to the construction and decommissioning phases can be considered non-significant. This is because the operation of the facility is considered more relevant to the impact categories than the other phases (Lassaux et al., 2007; Lundie et al., 2004). All mass and energy flows of the different sludge lines were quantified. Figure 2.2 shows the system boundaries for the sludge lines. SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 72 Figure 2.2. System boundaries of the different case studies CHAPTER 2: IDENTIFYING ENVIRONMENTAL AND ECONOMIC BARRIERS ASSOCIATED WITH THE SCALE OF OPERATION IN THE ANAEROBIC DIGESTION PROCESS 73 2.2.4. Life cycle inventory approach Inventories were performed with primary (real data coming from the different sludge lines) and secondary data (estimated and bibliographic data). Primary data are associated to the characteristics of sludge such as nitrogen, phosphorus or heavy metals, electricity consumption and biogas production of the different plants. Secondary data comprise air emissions from the AD unit or sludge applied in agriculture (De Vries et al., 2012). In addition, the data were completed with the Ecoinvent 3.5 database (Weidema et al., 2013). Several simplifications were considered to make a more reliable LCI. All these data are presented in Table 2.1 (main inputs to the sludge lines) and Table 2.2 (main outputs to the systems). The Spanish electricity mix has been updated with the most recent scenario according to the annual report of Red Eléctrica Española (REE, 2018). In addition, transmission losses associated to the electricity were taken into account. Euro 4 trucks with a capacity between 16 and 32 t were selected for the transport of chemicals and sludge. An average of 25 km was selected as a medium distance (Hospido et al., 2004). Biogas losses were estimated at 1.5% of the total biogas production (Lijó et al., 2017) and air emissions associated with the application of sludge to the soil as fertiliser and to the composting plant were calculated according to the literature (Boldrin et al., 2009). SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 80 Figure 2.3. Comparison of the CC outcomes with and without biogas losses (FU: 1 ton of mixed sludge). Symbols: S0 (□): small plant; S1.1 and S2.1(o): medium plant without biogas losses; S1.2 and S2.2 (Δ): medium plant with biogas; S3.1 (◊): large plant with biogas losses; S3.2(◊): large plant without biogas losses. 2.3.2. Assessment of the feasibility of the anaerobic digestion (AD) unit Considering the interest in implementing small-sized AD units, this section considers two main objectives: (i) whether or not the AD unit improves the environmental profile in S0, and (ii) to study the importance of energy recovery in sludge treatment. The study was carried out for the CC category because this category is more sensitive and is directly related to energy consumption and biogas losses. As in the previous scenarios, biogas losses are estimated at 1.5% of the total biogas production. The results are shown in Figure 2.4. The integration of the AD unit shows an improvement in the environmental profile of around 10%. This positive effect is due to the production of biogas that allows a partial autonomy of the use of energy from the grid. This also means that, from an environmental point of view, the AD technology will be appropriate for this plant size. 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0 200,000 400,000 600,000 800,000 1,000,000 1,200,000 CC [ kg CO2eq/ FU] h-e S0 S1.2 S1.1 S2.1 S2.2 S3.2 S3.1 CHAPTER 2: IDENTIFYING ENVIRONMENTAL AND ECONOMIC BARRIERS ASSOCIATED WITH THE SCALE OF OPERATION IN THE ANAEROBIC DIGESTION PROCESS 81 Figure 2.4. Sensitivity analysis of the small plant with and without AD technology Some authors evaluate the incorporation of technologies such as UASB or AnMBRs in small communities (less than 2,000 equivalent inhabitants) because they can have benefits such as biogas production, which can make these small plants self-sufficient in terms of energy (Kujawa-Roeleveld et al., 2006; Pretel et al., 2016). However, for the treatment of primary and secondary sludge in this type of plant, extensive information on the operational limit in terms of size is not available. Pavan et al. (2007) studied the efficiency of AD technology with a population equivalent range of 1,000 to 3,000 inhabitants. However, this sludge was mixed with municipal solid waste. Therefore, for the AD technology to be appropriate on a smaller scale, it would be necessary to operate with a higher organic load, such as mixing sewage sludge with agricultural waste. The need to implement a cogeneration system suitable for smaller digester sizes should also be considered to ensure biogas valorisation. This comment points out a recurrent situation in many WWTPs, where biogas is produced and burned directly in a torch. In this sense, it is important to highlight the role of energy production in achieving the water-energy nexus. The results of this analysis (two medium and one large plants) are shown in Figure 2.5. If biogas is not used in the WWTPs, 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 S0 CC [kg CO2eq/FU] SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 82 not only can the environmentally impacts increase, but also the operating costs. In S1, environmental impacts may increase by 10%; in the case of the other plants, this increase in impacts is even greater: about 33% in S2 and 28% in S3. These results show the importance of biogas valorisation, which is crucial in the eco-efficiency profile of WWTPs. Figure 2.5. Sensitivity analysis of the different plant sizes considering or not the energy use. Symbols: (Δ) without energy recovery; (o) with energy recovery 2.3.3. Energy benefit in the different sludge lines To evaluate the energy benefit of different sludge lines, an indicator called Energy Return on Investment (EROI) was calculated. This indicator is useful to calculate the energy produced in the sludge line in relation to the energy consumed in the sludge line itself. If the indicator is higher than 1, the plant has a positive energy balance, which makes it energy self-sufficient. However, if the indicator is less than 1, the plant is not energy efficient. EROI indicator is represented by Eq.1 (Bisinella de Faria et al., 2015): EROI= Electricity produced Electricity consumed [1] 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 S1 S2 S3 CC [kg CO2eq/FU] CHAPTER 2: IDENTIFYING ENVIRONMENTAL AND ECONOMIC BARRIERS ASSOCIATED WITH THE SCALE OF OPERATION IN THE ANAEROBIC DIGESTION PROCESS 83 Therefore, if the small plant has no AD unit, its EROI value is zero because there is no electricity production. However, when the AD unit is incorporated into the sludge line, the EROI value changes and is approximately 0.13, this means that about 13% of the electricity can be supplied by the biogas transformed into electricity. As for the other plants, the EROI values for medium-sized plants are 0.39 (S1) and 1.41 (S2). Finally, the value for the large plant is 1.19 (S3). According to these values, for S2 and S3 it is not necessary to consume energy from the grid in the sludge line. In addition, the management of the plant is crucial to have a satisfactory sludge-energy nexus. The difference between S1 and S2 are very significant when both plants are considered medium-sized plants. Therefore, to recover biogas and energy the plants must be properly managed. 2.3.4. Economic analysis of the different sludge lines From the perspective of economic analysis, operational costs are different from those obtained by considering the environmental impacts (Figure 2.5). Consequently, the large plant (S3) presents the best economic results with an approximate value of 50 €/ton of mixed sludge, followed by the medium-sized plants with approximate values of 50- 71€/ton of mixed sludge. The use of biogas in the plant itself can result in a benefit of between 11 and 9 €/ton of mixed sludge. These values are very important for reducing the operational costs. In the small plant lacking the AD unit, costs are higher (107 €/ton of mixed sludge). This can result in about 30% more in overall operating costs. In addition, in the small plant, there is a higher consumption of polyelectrolyte to achieve adequate sludge dewatering. Thus, if only the consumption of chemicals is compared, the operating costs increase by 98% compared to the rest of the plants. Finally, operating costs related to sludge disposal are higher in the medium and large plants. This makes sense because the amount of sludge that needs to be managed, especially in the larger plant. The trend in small plants may change when the AD unit is incorporated into the sludge scheme. If the biogas is recovered and used in the plant, the total operational costs can be reduced by 10%. This reduction is not only due to the biogas production, but it also to the reduction of polyelectrolyte SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 84 consumption, which also reduces the indirect emissions associated with the chemical consumption. Thus, the AD technology reduces operating costs, and the largest plant presents the most favourable costs. Despite the positive economic indicators, Kalbar et al., (2012) argue that the AD technology cannot be implemented at all scales because the amount of sludge must be sufficient and guaranteed. In this sense, there are other residues such as agricultural, livestock or food waste. If this type of waste is introduced in the AD unit, the production of biogas will be higher, and the benefits will increase between 0.05 and 0.20 €/kWh of electricity generated. The range is very different because, as already mentioned, the type of waste is very important. For example, manure cannot have an acceptable efficiency in the AD unit due to the amount of water it contains (Vasco-Correa et al., 2018). In addition, these economic costs take into account the benefits of using sludge as biofertiliser. Figure 2.5. Comparison of the economic results from the different plant sizes (FU: 1 ton of mixed sludge). Symbols: □ small plant, o medium plant (scenario 1), Δ medium plant (scenario 2), ◊ large plant In other words, the savings from not having to purchase mineral fertilisers, which can be around 50% of the total costs of fertilisers 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0 200 400 600 800 1,000 1,200 OPEX [€/FU] 1000 m h-e S0 S1 S2 S3 CHAPTER 2: IDENTIFYING ENVIRONMENTAL AND ECONOMIC BARRIERS ASSOCIATED WITH THE SCALE OF OPERATION IN THE ANAEROBIC DIGESTION PROCESS 85 (Frank, 1998). As mentioned above, a plant size of 25,000 equivalent inhabitants cannot be considered as a small plant. It is true that, in this case, the use of resources such as biogas or biofertilisers have a high variability costs and are more limited. This is because it is difficult to quantify the benefits of these products because sometimes the technology is not appropriate and does not allow the transformation of biogas into energy or the use of biofertilisers in agriculture (Borrion et al., 2012). 2.4. CONCLUSIONS The AD technology proved to be a viable alternative in sludge treatment due to the generation of a green energy and a quality digestate that can be used in agriculture. However, this technology is not integrated in all plant sizes and is attributed to the need for a minimum scale. This study showed that the AD unit is a suitable environmental and economic alternative for sludge treatment, regardless of the plant size. Moreover, the use of biogas in the plant itself can improve the eco-efficiency of the WWTPs due to less dependence on the energy from the grid. This means less CO2 emissions associated with non-renewable energy. In addition, the technological feasibility of the AD technology can be guaranteed in small plants as sewage sludge management could be combined with agricultural solid waste, which also implies a higher organic load in the digester and increased biogas production. 2.5. REFERENCES Bisinella de Faria, A.B., Spérandio, M., Ahmadi, A., Tiruta-Barna, L., 2015. Evaluation of new alternatives in wastewater treatment plants based on dynamic modelling and life cycle assessment (DM-LCA). Water Res. 84, 99– 111. https://doi.org/10.1016/j.watres.2015.06.048 Boldrin, A., Andersen, J.K., Møller, J., Christensen, T.H., Favoino, E., 2009. Composting and compost utilization: Accounting of greenhouse gases and global warming contributions. Waste Manag. Res. 27, 800–812. https://doi.org/10.1177/0734242X09345275 Borrion, A.L., McManus, M.C., Hammond, G.P., 2012. Environmental life cycle assessment of bioethanol production from wheat straw. Biomass and SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 86 Bioenergy 47, 9–19. https://doi.org/10.1016/j.biombioe.2012.10.017 De Vries, J.W., Groenestein, C.M., De Boer, I.J.M., 2012. Environmental consequences of processing manure to produce mineral fertilizer and bioenergy. J. Environ. Manage. 102, 173–183. https://doi.org/10.1016/ j.jenvman.2012.02.032 Dong, J., Chi, Y., Tang, Y., Wang, F., Huang, Q., 2014. Combined life cycle environmental and exergetic assessment of four typical sewage sludge treatment techniques in China. Energy and Fuels 28, 2114–2122. https://doi.org/10.1021/ef4024146 ECC, 1991. Directive 91/271/1991 ECC of 21 May 1991 concerning urban waste water treatment. Official Journal of the European Communities. Frank, R., 1998. The use of biosolids from wastewater treatment plants in agriculture. Environ. Manag. Heal. 9, 165–169. https://doi.org/10.1108/ 09566169810228926 Gude, V.G., 2015. Energy and water autarky of wastewater treatment and power generation systems. Renew. Sustain. Energy Rev. 45, 52–68. https://doi.org/10.1016/j.rser.2015.01.055 Guinée, J., 2002. Handbook on Life Cycle Assessment Operational Guide to the ISO Standards. Environ. Impact Assess. Rev. 23, 129–130. https://doi.org/10.1016/S0195-9255(02)00101-4 Hospido, A., Moreira, M.T., Fernández-Couto, M., Feijoo, G., 2004. Environmental performance of a municipal wastewater treatment plant. Int. J. Life Cycle Assess. 9, 261–271. https://doi.org/10.1007/BF02978602 Huijbregts, M.A.J., Steinmann, Z.J.N., Elshout, P.M.F., Stam, G., Verones, F., Vieira, M.D.M., Hollander, A., Zijp, M., van Zelm, R., 2017. ReCiPe 2016 v1.1. Kalbar, P.P., Karmakar, S., Asolekar, S.R., 2012. Technology assessment for wastewater treatment using multiple-attribute decision-making. Technol. Soc. 34, 295–302. https://doi.org/10.1016/j.techsoc.2012.10.001 Karagiannidis, A., Perkoulidis, G., 2009. A multi-criteria ranking of different technologies for the anaerobic digestion for energy recovery of the organic fraction of municipal solid wastes. Bioresour. Technol. 100, 2355–2360. https://doi.org/10.1016/j.biortech.2008.11.033 CHAPTER 2: IDENTIFYING ENVIRONMENTAL AND ECONOMIC BARRIERS ASSOCIATED WITH THE SCALE OF OPERATION IN THE ANAEROBIC DIGESTION PROCESS 87 Kujawa-Roeleveld, K., Elmitwalli, T., Zeeman, G., 2006. Enhanced primary treatment of concentrated black water and kitchen residues within DESAR concept using two types of anaerobic digesters. Water Sci. Technol. 53, 159–168. https://doi.org/10.2166/wst.2006.265 Lassaux, S., Renzoni, R., Germain, A., 2007. Life cycle assessment of water from the pumping station to the wastewater treatment plant. Int. J. Life Cycle Assess. 12, 118–126. https://doi.org/10.1065/lca2005.12.243 Lijó, L., Malamis, S., González-García, S., Moreira, M.T., Fatone, F., Katsou, E., 2017. Decentralised schemes for integrated management of wastewater and domestic organic waste: the case of a small community. J. Environ. Manage. 203, 732–740. https://doi.org/10.1016/j.jenvman.2016.11.053 Lorenzo-Toja, Y., Vázquez-Rowe, I., Amores, M.J., Termes-Rifé, M., Marín- Navarro, D., Moreira, M.T., Feijoo, G., 2016. Benchmarking wastewater treatment plants under an eco-efficiency perspective. Sci. Total Environ. 566–567, 468–479. https://doi.org/10.1016/j.scitotenv.2016.05.110 Lundie, S., Peters, G.M., Beavis, P.C., 2004. Life Cycle Assessment for Sustainable Metropolitan Water Systems Planning. Environ. Sci. Technol. 38, 3465– 3473. https://doi.org/10.1021/es034206m Nelson, K.L., Murray, A., Horvart, A., 2008. Hybrid Life-Cycle Environmental and Cost Inventory of Sewage Sludge Treatment and End-Use Scenarios : A Case Study from China 42, 3163–3169. Pan, S.-Y., Du, M.A., Huang, I.-T., Liu, I.-H., Chang, E.-E., Chiang, P.-C., 2015. Strategies on implementation of waste-to-energy (WTE) supply chain for circular economy system: a review. J. Clean. Prod. 108, 409–421. https://doi.org/10.1016/j.jclepro.2015.06.124 Pavan, P., Bolzonella, D., Battistoni, E., Cecchi, F., 2007. Anaerobic co-digestion of sludge with other organic wastes in small wastewater treatment plants: An economic considerations evaluation. Water Sci. Technol. 56, 45–53. https://doi.org/10.2166/wst.2007.730 Pretel, R., Robles, A., Ruano, M. V., Seco, A., Ferrer, J., 2016. Economic and environmental sustainability of submerged anaerobic MBR-based (AnMBR-based) technology as compared to aerobic-based technologies for moderate-/high-loaded urban wastewater treatment. J. Environ. Manage. 166, 45–54. https://doi.org/10.1016/j.jenvman.2015.10.004 REE, 2018. El sistema eléctrico español, 2018. Annual report SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 88 Rodriguez-Garcia, G., Molinos-Senante, M., Hospido, A., Hernández-Sancho, F., Moreira, M.T., Feijoo, G., 2011. Environmental and economic profile of six typologies of wastewater treatment plants. Water Res. 45, 5997–6010. https://doi.org/10.1016/j.watres.2011.08.053 Termes-Rifé, M., Molinos-Senante, M., Hernández-Sancho, F., Sala-Garrido, R., 2013. Life cycle costing: A tool to manage the urban water cycle. J. Water Supply Res. Tech. 62, 468–476. https://doi.org/10.2166/ aqua.2013.110 Vasco-Correa, J., Khanal, S., Manandhar, A., Shah, A., 2018. Anaerobic digestion for bioenergy production: Global status, environmental and technoeconomic implications, and government policies. Bioresour. Technol. 247, 1015–1026. https://doi.org/10.1016/j.biortech.2017.09.004 Weidema, B.P., Bauer, C., Hischier, R., Nemecek, T., Reinhard, J., Vadenbo, C.O., Wernet, G., 2013. Overview and methodology. Data quality guideline for the ecoinvent database version 3. Swiss Cent. Life Cycle Invent. St. Gall. Andrea Arias*a, Gumersindo Feijooa, María Teresa Moreiraa. “Benchmarking environmental and economic indicators of sludge management alternatives aimed at enhanced energy efficiency and nutrient recovery”. Journal of Environmental Management 2020 Nov 4; 111594. https://doi.org/10.1016/j.jenvman.2020.111594. aCRETUS institute. Department of Chemical Engineering. Universidade de Santiago de Compostela, E-15782, Santiago de Compostela, Galicia, Spain CHAPTER 3: Benchmarking environmental and economic indicators of sludge management alternatives aimed at enhancing energy efficiency and nutrient recovery SUMMARY The main objectives of a WWTP are to remove the pollutants present in the wastewater, reduce the volume of sludge and improve the energy efficiency. The sludge treatment has a relevant role within the overall management scheme and can imply the largest share in operational costs. Considering the sludge treatment as a key factor to improve in a WWTP, the main goal of this Chapter is to evaluate different alternatives and strategies for sludge management and treatment from the perspective of LCA, with special emphasis on those options that reduce the environmental impacts and economic costs. Two pre-treatments (one chemical and another thermal) and two post-treatments (composting unit followed by land application or incineration) were evaluated to improve the efficiency of the AD unit in terms of operation (biogas production and digested sludge), environmental and economic indicators. According to the results obtained, both sludge pre-treatments alternatives proved to be an adequate alternative to improve biogas production without negatively affecting environmental and economic impacts. If the final disposal of the digestate is analysed, its application to the soil as a biofertiliser is recommended, since it presents a better environmental profile than incineration. Nevertheless, soil application must be conducted under controlled conditions, avoiding exceeding the soil oversaturation, not only due to the potential eutrophication problems, but also to the presence of heavy metals that can lead to toxicity problems. SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 96 Table 3.1. Main inputs to the different systems (FU: 1 ton of mixed sludge). Scenario a) composting plant; Scenario b) incineration plant Scenario 0 Scenario 1 Scenario 2 Inputs from the technosphere Materials and fuel Influent TS (kg) 100 100 100 VS (kg) 70 70 70 COD (kg) 126 126 126 TN (kg) 3.70 3.70 3.70 TP (kg) 6.90 6.90 6.90 Electricity consumption Thickening (kWh) 21.67 21.67 21.67 TH (kWh) − − 12.5 Chemical pre-treatment (kWh) − 0.97 − AD (kWh) 15.85 10.39 10.39 Dewatering (kWh) 5.46 3.58 3.58 Composting (kWh)a 1.30 1.30 − Incineration (kWh)b 16.80 16.80 16.80 Chemical consumption Pre-treatment KOH (kg) − 9.63 − Dewatering Polyelectrolyte (kg) 1.60 1.60 1.60 Transport Polyelectrolyte (kg·km) 40 40 40 KOH (kg·km) − 24.20 − Sludge (kg·km)a 9.15 6.97 6.97 Ashes (kg∙km)b 1.45 1.45 1.45 Landfill Amount of ashes (kg)b 5.79∙10-2 5.79∙10-2 5.79∙10-2 Land application Agricultural machinery(kg)a 0.37 0.28 0.28 CHAPTER 3: BENCHMARKING ENVIRONMENTAL AND ECONOMIC INDICATORS OF SLUDGE MANAGEMENT ALTERNATIVES 97 Table 3.2. Main inputs to the different systems (FU: 1 ton of mixed sludge). Scenario a) composting plant; Scenario b) incineration plant Scenario 0 Scenario 1 Scenario 2 Outputs to the environment Emissions to air AD CH4 (kg) 0.43 0.69 0.87 CO2 (kg) 0.84 1.35 1.70 H2S (kg) 0.01 0.02 0.03 Composting unit a CH4 (kg) 0.53 0.53 − CO2 (kg) 13.78 13.78 − N2O (kg) 8.88∙10-3 0.01 − NH3 (kg) 0.26 0.26 − Land application a N2O (kg) 8.24 4.71 5.23 NH3 (kg) 4.93 3.88 4.31 Emissions to water Land application a NO3- (kg) 5.50 3.14 3.49 PO43- (kg) 4.26 2.43 2.43 Emissions to soil Land application a TN (kg) 2.00 2.00 2.00 TP (kg) 7.94 7.94 7.94 Cr (mg) 22.34 22.34 22.34 Fe (mg) 5676 5676 5676 Cu (mg) 603.49 603.49 603.49 Zn (mg) 754.49 754.49 754.49 As (mg) 9.21 9.21 9.21 Hg (mg) 0.95 0.95 0.95 Pb (mg) 51.07 51.07 51.07 Outputs to the technosphere Cogeneration Avoided electricity (kWh) 109 123.48 152.81 Avoided heat (kWh) 98.83 105.04 137.53 SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 98 3.2.3. Environmental and economic indicators for the sludge pretreatments The different impacts were evaluated through two methods. EP was calculated using the CML 2001 method (Guinée, 2002), while CC, OD, TA, PMF, HT, TET, FET, MET, and FD were calculated using the ReCiPe Midpoint (H) method (Huijbregts et al., 2017). As in previous chapters, the main reason for choosing two methodologies is based on how to estimate the impact of the COD contribution. Costs can be divided into operational and capital costs. The costs of construction, equipment or maintenance were calculated based on bibliographic data (Tables 3.3 and 3.4). In addition, in the operational costs, the disposal of sludge, electricity, chemical consumption and staff costs were included. Biogas that is transformed into electricity and heat was considered a benefit. In other words, the share of the total electricity from biogas will cover a fraction of the total requirements of the plant. The value of this electricity production is shown in Table 3.2. Thus, considering the price of electricity in Spain, this electricity production will be deducted from the total cost of electricity (Mills et al., 2014). Furthermore, in order to share the same FU as in the LCA methodology, the total costs are estimated per 1 ton of mixed sludge. The costs are represented by the Net Present Value (NPV) defined in Eq.1, where n is the time of useful life while i is the discount rate adjustment for inflation equal to 5% (Hermelink and Jarger, 2015). NPV= CAPEX + ∑ 𝑂𝑃𝐸𝑋 (1+𝑖)𝑛 𝑛 [1] In addition, in this study, it is important to calculate the payback time according to Eq.2, where Ms. represents the mass of sludge production in a year (ton/year); Cd is the value related to the costs of the final disposal of the sludge in €/ton; ΔE is the difference in the electricity (production in the sludge line (kWh/year); Ce: costs of electricity is associated with the price of electricity and C represents the total capital costs. CHAPTER 3: BENCHMARKING ENVIRONMENTAL AND ECONOMIC INDICATORS OF SLUDGE MANAGEMENT ALTERNATIVES 99 Payback time=𝑀𝑠 𝑥 𝐶𝑑+𝛥𝐸 𝑥 𝐶𝑒−𝐶 𝐼𝑛𝑣𝑒𝑠𝑡𝑚𝑒𝑛𝑡 𝑐𝑜𝑠𝑡 [2] Table 3.3. Inventory data for operational costs Economic item Unit Value Source Specialized worker €/year 50,000 Longo et al., 2017 Unit cost of electric energy €/kWh 0.12 Morales et al., 2015 Unit cost of polyelectrolyte €/kg 1.8 Longo et al., 2017 Unit cost of KOH €/kg 0.65 Carrere et al., 2012 Unitary cost for sludge composting and application €/ton 90 Longo et al., 2017 Unitary cost for sludge incineration €/ton 354 Hong et al., 2009 Table 3.4. Inventory data for the construction and maintenance costs Economic item Unit Value Source Thickening unit € 185,162 Mills et al., 2014 Anaerobic digestion unit € 403,114 Mills et al., 2014 Cogeneration unit € 386,098 Mills et al., 2014 Dewatering + silo unit € 265,903 Mills et al., 2014 Chemical pre-treatment unit € 60,000 Diamantis et al., 2013 TH pre-treatment unit € 410,850 Mills et al., 2014 Composting unit € 385,500 Chen, 2016 Incineration unit € 1,925,000 Panepinto et al., 2016 Project timeframe y 20 Mills et al., 2014 Interest rate % 5 Longo et al., 2017 Maintenance costs for civil works € 0.17 Hernández et al., 2006 Maintenance costs for electro-mechanic elements € 1.24 Hernández et al., 2006 SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 100 3.3. RESULTS AND DISCUSSION 3.3.1. Main parameters and life cycle results of the different sludge scenarios Table 3.5 presents the main variables and parameters associated with the scenarios considered in terms of energy consumption, biogas production from the primary sludge of the clarifying unit and from the secondary sludge of the activated sludge process in terms of methane and electricity, as well as the reduction in the volume of sludge. S2 (TH pre-treatment) presents the best results in terms of biogas production, followed by S1 (chemical pre-treatment). These pretreatments can improve electricity production between 6% and 11% compared to the baseline scenario. In addition, the degradability of sludge improves by 30% when a pre-treatment is included in the sludge line. For S0 (AD only) and S1 (chemical pre-treatment), energy consumption is very similar as it must take into account that the amount of electricity associated with the dosing and mixing of chemicals is minor. The energy consumption of the TH pre-treatment is approximately 14% higher than in the other options. When the energy balance takes into account the final management of the sludge (incineration or composting followed by land application), composting presents a better energy balance than the incineration unit, which translates into differences of around 25% for this parameter. Finally, heat is used entirely to maintain the temperature of the AD unit at 35°C. CHAPTER 3: BENCHMARKING ENVIRONMENTAL AND ECONOMIC INDICATORS OF SLUDGE MANAGEMENT ALTERNATIVES 101 Table 3.5. Variables and operational parameters associated to the scenarios considered including final disposal of the sludge (FU: 1 ton of mixed sludge). Scenarios: a) composting and land application; b) incineration. Scenario 0 Scenario 1 Scenario 2 Energy consumption a (kWh) 61.08 54.71 64.94 Energy consumption b (kWh) 221.88 214.77 224.94 Biogas production (m3) 54.04 57.44 75.21 Methane yield (m3 CH4/kgVS feed) Primary sludge 0.30 0.33 0.38 Secondary sludge 0.20 0.28 0.31 Electricity production (kWh) 109 123.48 152.81 Energy balance (kWh) a -47.92 -68.77 -87.87 Energy balance (kWh) b 112.88 91.23 72.31 Heat production (kWh) 98.83 105.04 137.53 Sludge production (kg/d) 22876 17435 17435 The environmental profile is reported in terms of various impact categories (Table 3.6). The results show that the environmental impacts are very different depending on the category considered. In the case of chemical pre-treatment, greater environmental impacts are observed in categories such as TA, PMF and TET due to the indirect emissions associated with chemical production. However, when the TH and chemical pre-treatment are implemented in the sludge line, the avoided electricity may increase due to the greater amount of biogas, provided that the valorisation of biogas entails lower dependence of grid electricity. In addition, in S2a (TH pre-treatment), the composting plant is not necessary because, according to Directive 86/278/CEE, thermallytreated digested sludge can be applied directly to agriculture. In addition, impacts related to atmospheric emissions associated with the composting unit can be avoided (Table 3.2). However, it is very difficult to know the overall environmental impact of these pre-treatments due to the much larger impacts of the post-treatments. In energy-dependent categories such as CC, OD or FD, the incineration unit has greater impacts than the composting unit followed SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 102 by land application. This is due to the large amount of electricity consumed in this process. Indirect emissions are related to fossil CO2 and N2O from the coal electricity production. Conversely, scenarios with composting followed by land application present worse environmental profile than the incineration process in toxicity-related categories due to the presence of heavy metals in the sludge. In this case, only the heavy metals in the sludge were considered since the routine measurement of micropollutants is not carried out due to the complexity of the necessary equipment, sample preparation and costs. If the pathogens or micropollutants were included in this study, the toxicity categories would probably be the most affected, considering the application of the sludge to the soil. However, although, for the toxicity impact categories, the impact would be higher, the environmental profile in overall terms will not change as incineration continues to be the main factor with the greatest weight in the energy-dependent categories. As far as toxicity is concerned, it is important to be aware that when the TH pre-treatment is applied, the sludge can be considered sterilised. In this sense, the pathogens present in the sludge would be removed and its application would be safe. CHAPTER 3: BENCHMARKING ENVIRONMENTAL AND ECONOMIC INDICATORS OF SLUDGE MANAGEMENT ALTERNATIVES 103 Table 3.6. Characterisation results for the different scenarios evaluated in this study (including post-treatment) for 1 ton of mixed sludge. a) composting plant; b) incineration plant I.C Scenario 0 Scenario 1 Scenario 2 A B A B A B CC 40.82 160.50 42.56 162.22 29.41 167.66 OD 8.3·10-5 9.1·10-6 9.6·10-5 9.2·10-5 1.1·10-5 9.3·10-5 TA 0.48 0.77 0.48 0.76 -0.08 0.73 EP 25.77 0.20 25.77 0.20 25.77 0.20 HT 115.62 4.17 115.60 4.15 115.32 3.88 PMF 0.03 0.29 0.03 0.29 -0.05 0.27 TET 43.80 173.75 43.76 173.71 31.58 162.20 FET 6260 3.24 6260 3.24 6260 3.24 MET 4877 4.30 4877 4.30 4877 4.30 FD -3.10 31.43 -3.28 31.50 -5.29 29.34 SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 104 In order to discern the contribution of pre-treatment to the overall impact, two analysis were proposed. The main environmental categories in WWTPs are CC and EP (Rodriguez-Garcia et al., 2011). However, the EP category is more affected by the sludge disposal and, in this case, was not taken into account. For this reason, the CC category was evaluated for the different scenarios (conventional, chemical pre-treatment and TH pretreatment). In addition, the main sub-systems that contributes to the environmental profile were evaluated in this category. For the CC category (especially relevant in processes depending on energy production and use), S1 presents the best environmental results because chemical pre-treatment does not require much energy followed by the TH pre-treatment. The worst scenario is the conventional one (Figure 3.2) because the biogas production is lower than in the other scenarios. Although the conventional scenario has lower energy consumption due to the lack of pre-treatment unit, biogas production is lower than in the other scenarios, which results in worse environmental profile. Furthermore, considering the CC impact of the sub-systems, of each scenario (Figure 3.2), the AD unit has the worst environmental impacts due to CH4, CO2 and H2S emissions (Table 3.2) while the impact of chemical pre-treatment is considered negligible in this category. However, for S2 the impact of the energy consumption for the TH pretreatment represents 6% in this category. CHAPTER 3: BENCHMARKING ENVIRONMENTAL AND ECONOMIC INDICATORS OF SLUDGE MANAGEMENT ALTERNATIVES 105 Figure 3.2. Environmental results for the climate change (CC) category for the different scenarios analysed. S0 (conventional scenario); S1 (chemical pretreatment) and S2 (TH pre-treatment) SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 112 3.4. CONCLUSIONS The AD process is nowadays the most widespread process for the management of sewage sludge as it allows the production of bioenergy and the stabilisation of the sludge. Even though it is a mature and widely implemented technology, it is necessary to improve the process performance by increasing the biogas yield so this energy can be used in the plant itself. In this context, several pre-treatments have proven to have beneficial effects on biogas production: 12% (for chemically enhanced precipitation) and 30% (for TH). Additionally, the degradability of sludge and life cycle environmental impacts are significantly improved. Although construction costs increase when the sludge pre-treatment is incorporated into the sludge line, the payback time is reduced compared to the conventional configuration. This implies that amortisation of these sludge lines is more feasible compared to the conventional case. Finally, the land application of the sludge has a better environmental and economic profile than the incineration unit. However, the presence of heavy metals must be controlled and measured to avoid toxicity impacts in this sludge disposal scheme. 3.5. REFERENCES Abelleira-Pereira, J.M., Pérez-Elvira, S.I., Sánchez-Oneto, J., de la Cruz, R., Portela, J.R., Nebot, E., 2015. Enhancement of methane production in mesophilic anaerobic digestion of secondary sewage sludge by advanced thermal hydrolysis pretreatment. Water Res. 71, 330–340. https://doi.org/ 10.1016/j.watres.2014.12.027 Appels, L., Houtmeyers, S., Degrève, J., Impe, J. Van, Dewil, R., 2013. Bioresource Technology Influence of microwave pre-treatment on sludge solubilization and pilot scale semi-continuous anaerobic digestion. Bioresour. Technol. 128, 598–603. https://doi.org/10.1016/j.biortech.2012.11.007 Ariunbaatar, J., Panico, A., Esposito, G., Pirozzi, F., Lens, P.N.L., 2014. Pretreatment methods to enhance anaerobic digestion of organic solid waste. Appl. Energy 123, 143–156. https://doi.org/10.1016/j.apenergy. 2014.02.035 CHAPTER 3: BENCHMARKING ENVIRONMENTAL AND ECONOMIC INDICATORS OF SLUDGE MANAGEMENT ALTERNATIVES 113 Boldrin, A., Andersen, J.K., Møller, J., Christensen, T.H., Favoino, E., 2009. Composting and compost utilization: Accounting of greenhouse gases and global warming contributions. Waste Manag. Res. 27, 800–812. https://doi.org/10.1177/0734242X09345275 Bruun, S., Hansen, T.L., Christensen, T.H., Magid, J., Jensen, L.S., 2006. Application of processed organic municipal solid waste on agricultural land - A scenario analysis. Environ. Model. Assess. 11, 251–265. https://doi.org/10.1007/ s10666-005-9028-0 Cano, R., Pérez-Elvira, S., Fernádez-Polanco, F., 2015. Energy feasibility study of sludge pretreatments : A review. Appl. Energy 149, 176–185. https://doi.org/10.1016/j.apenergy.2015.03.132 Cao, Y., Pawłowski, A., 2013. Life cycle assessment of two emerging sewage sludge-to-energy systems: Evaluating energy and greenhouse gas emissions implications. Bioresour. Technol. 127, 81–91. https://doi.org/ 10.1016/j.biortech.2012.09.135 Carrere, H., Rafrafi, Y., Battimelli, A., Torrijos, M., Delgenes, J.P., Motte, C., 2012. Improving methane production during the codigestion of waste-activated sludge and fatty wastewater : Impact of thermo-alkaline pretreatment on batch and semi-continuous processes. Chem. Eng. J. 210, 404–409. https://doi.org/10.1016/j.cej.2012.09.005 Chen, Y., 2016. A Cost Analysis of Food Waste Composting in Taiwan. https://doi.org/10.3390/su8111210 Colosi, L.M., Resurreccion, E.P., Zhang, Y., 2015. Assessing the energy and environmental performance of algae-mediated tertiary treatment of estrogenic compounds. Environ. Sci. Process. Impacts 17, 421–428. https://doi.org/10.1039/c4em00541d Corominas, L., Foley, J., Guest, J.S., Hospido, A., Larsen, H.F., Morera, S., Shaw, A., 2013. Life cycle assessment applied to wastewater treatment: State of the art. Water Res. 47, 5480–5492. https://doi.org/10.1016/j.watres.2013. 06.049 Diamantis, V., Verstraete, W., Eftaxias, A., Bundervoet, B., Siegfried, V., Melidis, P., Aivasidis, A., 2013. Sewage pre-concentration for maximum recovery and reuse at decentralized level 1188–1193. https://doi.org/10.2166/ wst.2013.639 SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 114 Dones R., Bauer C., Bolliger R., Burger B., Faist Emmenegger M., Frischknecht R., Heck T., Jungbluth N., Röder A., T.M., 2007. Life cycle inventories of energy systems: results of current systems in Switzerland and other UCTE countries. Ecoinvent Rep.5. https://doi.org/10.1007/s11367-014-0838-7 Dong, J., Chi, Y., Tang, Y., Wang, F., Huang, Q., 2014. Combined life cycle environmental and exergetic assessment of four typical sewage sludge treatment techniques in China. Energy and Fuels 28, 2114–2122. https://doi.org/10.1021/ef4024146 Ebenezer, A.V., Arulazhagan, P., Kumar, S.A., Yeom, I., Banu, J.R., 2015. Effect of deflocculation on the efficiency of low-energy microwave pretreatment and anaerobic biodegradation of waste activated sludge. Appl. Energy 145, 104–110. https://doi.org/10.1016/j.apenergy.2015.01.133 European Communities, 1986. Council Directive of 12 June 1986 on the Protection of the Environment, and in Particular of the Soil, when Sewage Sludge is used in Agriculture. http://data.europa.eu/eli/dir/1986/278/oj Guinée, J., 2002. Handbook on Life Cycle Assessment Operational Guide to the ISO Standards. Environ. Impact Assess. Rev. 23, 129–130. https://doi.org/ 10.1016/S0195-9255(02)00101-4 Hermelink, A.., Jarger de, D., 2015. Evaluating Our Future: the Crucial Role of Discount Rates in European Commission Energy System Modelling [WWW Document]. http://www.eceee.org/policy-areas/discount-rates/ evaluating-our-future-report. Hernández, F., Urkiaga, A., Fuentes, L. De, Bis, B., Chiru, E., 2006. Feasibility studies for water reuse projects: an economical approach 187, 253–261. https://doi.org/10.1016/j.desal.2005.04.084 Hong, Jinglan, Hong, Jingmin, Otaki, M., Jolliet, O., 2009. Environmental and economic life cycle assessment for sewage sludge treatment processes in Japan. Waste Manag. 29, 696–703. https://doi.org/10.1016/j.wasman. 2008.03.026 Hospido, A., Moreira, M.T., Martín, M., Rigola, M., Feijoo, G., 2005. Environmental Evaluation of Different Treatment Processes for Sludge from Urban Wastewater Treatments : Anaerobic Digestion versus Thermal Processes 10, 336–345. Houillon, G., Jolliet, O., 2005. Life cycle assessment of processes for the treatment of wastewater urban sludge: Energy and global warming analysis. J. Clean. Prod. 13, 287–299. https://doi.org/10.1016/j.jclepro.2004.02.022 CHAPTER 3: BENCHMARKING ENVIRONMENTAL AND ECONOMIC INDICATORS OF SLUDGE MANAGEMENT ALTERNATIVES 115 Huijbregts, M.A.J., Steinmann, Z.J.N., Elshout, P.M.F., Stam, G., Verones, F., Vieira, M.D.M., Hollander, A., Zijp, M., van Zelm, R., 2017. ReCiPe 2016 v1.1. Jeongsik Kim, Park, C., Kim, T.-H., Lee, M., Kim, S., Seung-Wook, K., Lee, J., 2003. Effect of Various Pretreamtents to Enhanced Anaerobic Digestion with Waste Activated Sludge. J. Biosci. Bioeng. 95, 271–275. Kelessidis, A., Stasinakis, A.S., 2012. Comparative study of the methods used for treatment and final disposal of sewage sludge in European countries. Waste Manag. 32, 1186–1195. https://doi.org/10.1016/j.wasman. 2012.01.012 Kim, D., Lee, K., Park, K.Y., 2015. Enhancement of biogas production from anaerobic digestion of waste activated sludge by hydrothermal pretreatment. Int. Biodeterior. Biodegradation 101, 42–46. https://doi.org/ 10.1016/j.ibiod.2015.03.025 Lijó, L., Malamis, S., González-García, S., Moreira, M.T., Fatone, F., Katsou, E., 2017. Decentralised schemes for integrated management of wastewater and domestic organic waste: the case of a small community. J. Environ. Manage. 203, 732–740. https://doi.org/10.1016/j.jenvman.2016.11.053 Longo, S., Frison, N., Renzi, D., Fatone, F., Hospido, A., 2017. Is SCENA a good approach for side-stream integrated treatment from an environmental and economic point of view? Water Res. 125, 478–489. https://doi.org/ 10.1016/j.watres.2017.09.006 Lorenzo-Toja, Y., Alfonsín, C., Amores, M.J., Aldea, X., Marin, D., Moreira, M.T., Feijoo, G., 2016. Beyond the conventional life cycle inventory in wastewater treatment plants. Sci. Total Environ. 553, 71–82. https://doi.org/ 10.1016/j.scitotenv.2016.02.073 Ma, J., Duong, T.H., Smits, M., Verstraete, W., Carballa, M., 2011. Enhanced biomethanation of kitchen waste by different pre-treatments. Bioresour. Technol. 102, 592–599. https://doi.org/10.1016/j.biortech.2010.07.122 Martín, M.Á., González, I., Serrano, A., Siles, J.Á., 2015. Evaluation of the improvement of sonication pre-treatment in the anaerobic digestion of sewage sludge 147, 330–337. https://doi.org/10.1016/j.jenvman. 2014.09.022 Mills, N., Pearce, P., Farrow, J., Thorpe, R.B., Kirkby, N.F., 2014. Environmental & economic life cycle assessment of current & future sewage sludge to energy technologies. Waste Manag. 34, 185–195. https://doi.org/10.1016/ j.wasman.2013.08.024 SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 116 Morales, N., Val del Río, Á., Vázquez-Padín, J.R., Méndez, R., Mosquera-Corral, A., Campos, J.L., 2015. Integration of the Anammox process to the rejection water and main stream lines of WWTPs. Chemosphere 140, 99–105. https://doi.org/10.1016/j.chemosphere.2015.03.058 Murray, A., Horvath, A., Nelson, K.L., 2008. Hybrid life-cycle environmental and cost inventory of sewage sludge treatment and end-use scenarios: A case study from China. Environ. Sci. Technol. 42, 3163–3169. https://doi.org/ 10.1021/es702256w Panepinto, D., Fiore, S., Genon, G., Acri, M., 2016. Thermal valorization of sewer sludge : Perspectives for large wastewater treatment plants. J. Clean. Prod. 137, 1323–1329. https://doi.org/10.1016/j.jclepro.2016.08.014 Pérez-Elvira, S.I., Fernández-Polanco, F., 2012. Continuous thermal hydrolysis and anaerobic digestion of sludge. Energy integration study. Water Sci. Technol. 65, 1839–1846. https://doi.org/10.2166/wst.2012.863 Pérez-Elvira, S.I., Fernández-Polanco, F., 2008. Hydrothermal multivariable approach . Full-scale feasibility study 11. https://doi.org/10.2225/vol11- issue4-fulltext-14 Ra, R., Gorm, T., Nizami, A., Asam, Z., Murphy, J.D., Kiely, G., 2010. Effect of thermal, chemical and thermo-chemical pre-treatments to enhance methane production 35, 4556–4561. https://doi.org/10.1016/j.energy. 2010.07.011 REE, 2018. Spanish Power Systems 2018. Annual report. Riau, V., De la Rubia, M.A., Pérez, M., 2015. Upgrading the temperature-phased anaerobic digestion of waste activated sludge by ultrasonic pretreatment. Chem. Eng. J. 259, 672–681. https://doi.org/10.1016/j.cej.2014.08.032 Rittmann, B.E., Lee, H., Zhang, H., Alder, J., Banaszak, J.E., Lopez, R., 2008. Fullscale application of focused-pulsed pre-treatment for improving biosolids digestion and conversion to methane 1895–1902. https://doi.org/ 10.2166/wst.2008.547 Rodriguez-Garcia, G., Molinos-Senante, M., Hospido, A., Hernández-Sancho, F., Moreira, M.T., Feijoo, G., 2011. Environmental and economic profile of six typologies of wastewater treatment plants. Water Res. 45, 5997–6010. https://doi.org/10.1016/j.watres.2011.08.053 Salerno, M.B., Lee, H., Parameswaran, P., Rittmann, B.E., 2009. Using a Pulsed Electric Field as a Pretreatment for Improved Biosolids Digestion and Methanogenesis 831–839. https://doi.org/10.2175/106143009X407366 CHAPTER 3: BENCHMARKING ENVIRONMENTAL AND ECONOMIC INDICATORS OF SLUDGE MANAGEMENT ALTERNATIVES 117 Suh, Y., Rousseaux, P., 2001. An LCA of alternative wastewter sludge treatment scenarios. Resour. Conserv. Recycl. 35, 191–200. Tarantini, M., Buttol, P., Maiorino, L., 2007. An environmental LCA of alternative scenarios of urban sewage sludge treatment and disposal. Therm. Sci. 11, 153–164. https://doi.org/10.2298/TSCI0703153T Tchobanoglous, G., Burton, F., Stensel, H.D., 1998. Wastewater engineering: An Overview, in: Wastewater Engineering Treatment and Reuse. pp. 1–24. https://doi.org/10.1016/0309-1708(80)90067-6 Wei, W., Wang, Q., Zhang, L., Laloo, A., Duan, H., Batstone, D.J., Yuan, Z., 2018. Free nitrous acid pre-treatment of waste activated sludge enhances volatile solids destruction and improves sludge dewaterability in continuous anaerobic digestion. Water Res. 130, 13–19. https://doi.org/10.1016/ j.watres.2017.11.050 Wernet, G., Bauer, C., Steubing, B., Reinhard, J., Moreno-Ruiz, E., Weidema, B., 2016. The ecoinvent database version 3 (part I): overview and methodology. Int. J. Life Cycle Assess. 21, 1218–1230. https://doi.org/ 10.1007/s11367-016-1087-8 Xu, C., Chen, W., Hong, J., 2014. Life-cycle environmental and economic assessment of sewage sludge treatment in China. J. Clean. Prod. 67, 79–87. https://doi.org/10.1016/j.jclepro.2013.12.002 Andrea Arias*a, Gumersindo Feijooa, María Teresa Moreiraa. “Linking organic matter removal and biogas yield in the environmental profile of innovative wastewater treatment technologies”. Journal of Cleaner Production 2020 Vol.247, 124292. https://doi.org/10.1016/j.jclepro.2020.124292. a CRETUS institute. Department of Chemical Engineering. Universidade de Santiago de Compostela, E-15782, Santiago de Compostela, Galicia, Spain CHAPTER 4: Pursing energy self-sufficient in wastewater treatment plants: environmental and economic assessment of innovative options SUMMARY Nowadays, WWTPs should no longer be considered as end-of-pipe systems but should be approached by integrating standards of technological performance but also environmental, economic and social indicators. In this framework, it is necessary to address the energy-water nexus for the selection of the most appropriate technology. Targeting increased biogas yields, the recovery of OM in the primary treatment emerges as interesting alternative. For this purpose, new technologies such as RBFs or HRAS and other not so new as UASB has been implemented as primary treatment in the water line. Chapter 4 aims at identifying the life-cycle environmental impacts and economic costs associated to four configurations: three schemes focus on recovering OM in the primary treatment and one conventional using the LCA methodology. Despite the fact that the technological and operational complexity is noteworthy for OM-oriented process, lower environmental impacts were estimated for technologies such as UASB and HRAS. However, not all schemes based on OM recovery have environmental benefits and special attention should be paid to aspects associated with the chemical and energy consumption, as well as land occupation, which may be limiting variables to implement these technologies. SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 120 TABLE OF CONTENTS-CHAPTER 4 4.1. Introduction ............................................................................................ 121 4.2. Materials and methods ........................................................................ 123 4.2.1. Description of the wastewater schemes and scope of the study ................................................................................................................... 123 4.2.2. Inventory data acquisition for the new wastewater configurations ................................................................................................ 128 4.2.3. Impact assessment methodology and economic evaluation .............................................................................................................................. 132 4.3. Environmental and economic results ............................................ 132 4.3.1. Environmental and economic approach for the four studied scenarios ........................................................................................................... 132 4.3.2. Environmental perspective for each wastewater treatment configuration .................................................................................................. 136 4.4. Discussion ................................................................................................ 140 4.4.1. Improving wastewater treatment efficiency in the WWTPs .............................................................................................................................. 140 4.4.2. How conventional and new technologies influence the effluent quality ............................................................................................... 142 4.4.3. Economic aspects focused on energy recovery....................... 143 4.4.4. Sensitivity analysis of the functional unit (FU) ....................... 144 4.5. Conclusions ............................................................................................. 145 4.6. References ............................................................................................... 145 CHAPTER 4: PURSING ENERGY SELF-SUFFICIENT IN WASTEWATER TREATMENTS PLANTS: ENVIRONMENTAL AND ECONOMIC ASSESSMENT OF INNOVATIVE OPTIONS 121 4.1. INTRODUCTION In general, current WWTPs meet environmental requirements in terms of organic matter, nitrogen and phosphorus removal. However, it is becoming increasingly evident that wastewater technologies must address more complex challenges such as the safe removal of emerging contaminants such as recalcitrant compounds and pathogens, as well as efficient operation with less resource consumption (Barbosa et al., 2016; Gu et al., 2018). As was mentioned in Chapter 1, one of the hotspots in wastewater treatment is the energy consumption in aeration for the biological process (Gikas, 2017). In this framework, the Anammox process has several advantages such as the reduction of oxygen requirements, therefore, the energy requirement for aeration can be reduced. In addition, the extraordinarily low biomass yield of 0.12 kg VSS/ kg Nremoved means low sludge generation (Morales et al., 2015b). There are several schemes that have been developed in recent years, such as IFAS, SHARON or CANON (Malovanyy et al., 2015a; Van Dongen et al., 2001; Vázquez- Padín et al., 2010b). Although the strategy is the same for different technologies, the main difference between technologies is that PN- Anammox can be implemented in a single or two stages. However, these technologies encounter limitations in the case of streams with a large percentage of solids or a high C/N ratio (Xu et al., 2015). In this context, it is necessary to recover OM in primary treatment. In Chapter 1, these technologies such as HRAS, RBF, CEPT or UASB (Jimenez et al., 2015; Lotti et al., 2015) were explained. The choice of one or another technology and its combination depend on several factors. For example, the energy consumption associated with UASB implies its implementation in hot climates (Bdour et al., 2009) or RBF can be combined with technologies such as HRAS and CEPT but not with the Anammox process due to the high solid content (Ruiken et al., 2012). Sludge management is another decisive element in the operation of WWTPs according to the circular economy approach. Although the most applied methods are incineration and land application (Kelessidis and Stasinakis, 2012; Tomei et al., 2016), other options such as gasification, SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 128 4.2.2. Inventory data acquisition for the new wastewater configurations In this study, only the environmental impacts associated with the operational phase were evaluated. Although sewerage impacts contribute significantly to negative effect (Petit-Boix et al., 2014), the operational phase is the main cause of the environmental impacts. System boundaries were defined as the operation of the different scenarios that are defined in the previous section (Figure 4.1 to Figure 4.4). The simplest FU selected could be 1 m3 of treated wastewater. However, bearing in mind that the objective is to improve the efficiency of the WWTPs, 1 kWh of energy produced was selected as FU. LCI was carried out with estimated data related with the different technologies considered in the scenarios such as sludge, wastewater characteristics or consumption of chemicals, among others. In addition, the estimated data were completed with bibliographic data associated with the air emissions and heavy metals contained in the solid digestate (Hijazi et al., 2016; Lorenzo-Toja et al., 2016b) and the Ecoinvent v3.5 database (Wernet et al., 2016). The data used to build the inventories are presented in Table 4.1 (main inputs to the system) and Table 4.2 (main outputs to the system). Moreover, several simplifications have been considered to complete the inventory information. These simplifications are presented below: Transport: the distance for chemical and sludge distribution was selected as 25 km (Hospido et al., 2004). Moreover, trucks Euro 4 with a capacity between 16 to 32 t were selected as transport vehicles (Lorenzo- Toja et al., 2016b). Consumption of chemicals in the sludge line: the amount of polyelectrolyte consumed in the dewatering unit was 5-8 kg polymer/ 1000 kg of dry matter (Tchobanoglous et al., 1998). Air emissions from the compost unit: these emissions were calculated according to the type of composting plant selected. In this case, the open windrow activate ventilation process was selected as a composting process (Boldrin et al., 2009). CHAPTER 4: PURSING ENERGY SELF-SUFFICIENT IN WASTEWATER TREATMENTS PLANTS: ENVIRONMENTAL AND ECONOMIC ASSESSMENT OF INNOVATIVE OPTIONS 129 Electricity: Ecoinvent 3.5 database was updated to the 2018 Spanish country mix (REE, 2018). Moreover, the transmission losses associated with electricity transport were taken into account (Dones et al., 2007). Table 4.1. Summary of the inventory data for the four scenarios considered. FU: 1 kWh of produced energy S1 S2 S3 S4 Inputs from technosphere Materials and fuel Influent COD (g) 2632 2632 2941 8333 TN (g) 101.70 99.40 112.12 305.07 TP (g) 25.14 24.57 27.71 75.41 Cr (mg) 25.92 25.37 28.21 79.92 Mn (mg) 709.95 694.92 772.59 2189 Fe (mg) 14695.95 14384.92 15992.65 45312.50 Co (mg) 7.51 7.35 8.18 23.17 Ni (mg) 50.65 49.58 55.12 156.17 Cu (mg) 1997.27 1955 2173.50 6158.25 Zn (mg) 830.89 813.31 904.21 2591.92 As (mg) 28.16 25.57 30.65 86.83 Cd (mg) 2.00 1.96 2.18 6.17 Hg (mg) 1.35 1.32 1.47 4.17 Pb (mg) 46.68 45.69 50.79 143.92 Electricity consumption Pre-treatment (kWh) 0.08 0.08 0.09 0.24 UASB (kWh) 0.05 - - - RBF (kWh) - - 0.60 - CEPT (kWh) - - 0.06 - HRAS (kWh) - 0.16 - - PC (kWh) - - - 0.16 IFAS (kWh) 0.86 0.84 0.95 - CAS (kWh) - - - 3.40 Thickening (kWh) 3.46·10-2 0.03 0.04 0.10 AD (kWh) - 0.25 0.17 0.75 Dewatering (kWh) 2.79·10-3 2.72·10-3 3.07·10-4 5.67·10-4 Composting (kWh) 5.29·10-2 5.71·10-2 5.83·10-2 1.59·10-1 SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 130 Table 4.1. (cont.). Summary of the inventory data for the four scenarios considered. FU: 1 kWh of produced energy S1 S2 S3 S4 Chemical consumption CEPT FeCl3 (kg) - - 0.59 - Dewatering Polyelectrolyte (kg) 1.89·10-4 1.85·10-4 2.08·10-4 3.50·10-5 Transport Polyelectrolyte (kg·km) 4.72·10-3 4.62·10-3 5.21·10-3 5.67·10-4 FeCl3 (kg) - - 14.89 - Sludge (kg·km) 2.81 2.72 2.77 7.39 Land application Agricultural machinery (kg) 1.13·10-1 1.09·10-1 1.11·10-1 2.96·10-1 CHAPTER 4: PURSING ENERGY SELF-SUFFICIENT IN WASTEWATER TREATMENTS PLANTS: ENVIRONMENTAL AND ECONOMIC ASSESSMENT OF INNOVATIVE OPTIONS 131 Table 4.2. Summary of the inventory data for the four scenarios considered. FU: 1 kWh of produced energy S1 S2 S3 S4 Outputs to the environment Emissions to air AD CH4 (kg) 4.74·10-3 4.64·10-3 4.59·10-3 4.88·10-3 CO2 (kg) 9.37·10-3 9.17·10-3 8.84·10-3 9.63·10-3 H2S (kg) 1.65·10-4 1.62·10-4 1.56·10-4 1.70·10-4 Composting unit CH4 (kg) 5.96·10-3 5.51·10-3 2.67·10-3 6.38·10-3 CO2 (kg) 1.27 1.71 5.69·10-1 1.36 N2O (kg) 9.42·10-5 8.71·10-5 4.55·10-5 1.01·10-4 NH3 (kg) 1.28·10-2 1.18·10-2 6.19·10-3 1.37·10-2 Land application N2O (kg) 3.05·10-4 5.35·10-5 1.48·10-4 3.27·10-4 NH3 (kg) 2.52·10-4 4.41·10-5 1.22·10-4 2.70·10-4 Emissions to water NO3- (kg) 2.04·10-2 3.57·10-3 9.84·10-3 2.18·10-2 PO4-3 (kg) 2.56·10-3 4.47·10-4 1.19·10-3 2.56·10-3 Emissions to soil COD (kg) 1.24 1.15 5.57·10-1 1.33 TN (kg) 1.30·10-2 1.20·10-2 6.26·10-3 1.39·10-2 TP (kg) 8.35·10-2 7.71·10-2 3.88·10-2 8.37·10-2 Cr (mg) 79.16 77.49 86.15 244.10 Fe (mg) 20118 19692 21894 62032 Cu (mg) 2138 2093 2327 6595 Zn (mg) 2674 2617 2910 8245 As (mg) 32.65 31.96 35.53 100.67 Hg (mg) 3.35 3.28 3.65 10.33 Pb (mg) 181 177.17 196.97 558.08 SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 132 4.2.3. Impact assessment methodology and economic evaluation Environmental impacts and their corresponding prices were quantified through the SimaPro 9.0 software. Two methods were selected to measure the most representative impacts of the different scenarios considered. EP was calculated with the CML 2001 method (Guinée, 2002) whereas CC, PMF, HT, OD, FD, TA, TET, MET, FET and WC were calculated with the ReCiPE Midpoint (H) v1.1 (Huijbregts et al., 2017). Moreover, these impact categories were transformed into their environmental prices. However, not all categories have their transformation into costs, for this reason, WC and EP were not included in this study (De Bruyn et al., 2018). Operating and construction costs (OPEX + CAPEX) were selected as direct economic indicators, while environmental prices were quantified such as indirect indicators. Operational costs were related to sludge management, electricity, staff and chemical consumption. Regarding capital costs, construction, maintenance and depreciation costs were included. 4.3. ENVIRONMENTAL AND ECONOMIC RESULTS 4.3.1. Environmental and economic approach for the four studied scenarios The environmental results are presented as a comparison between the different scenarios considered (Table 4.3). The best scenarios are Scenario 1 (UASB + IFAS configuration) followed by Scenario 2 (HRAS + IFAS configuration) because there is more electricity production than in the others. In addition, the consumption of chemicals in these wastewater units (primary technologies) is zero. However, Scenario 3 (RBF + CEPT + IFAS scheme), which is a new scheme, has a high environmental impact, even higher than in the conventional system in several categories. These environmental impacts are due to the indirect emissions associated with the chemicals production. Thus, the addition of chemicals to improve biogas production, it is not a good option from an environmental point of view. In eutrophication and toxicity categories (EP, FET and MET), which depend on the quality of effluent, Scenario 4 (conventional system) CHAPTER 4: PURSING ENERGY SELF-SUFFICIENT IN WASTEWATER TREATMENTS PLANTS: ENVIRONMENTAL AND ECONOMIC ASSESSMENT OF INNOVATIVE OPTIONS 133 presents the worst results. The eutrophication impact is associated with the discharge of effluent into the aquatic environment as it contains N, P and COD. In addition, the integration of the IFAS unit can decrease by 13% the electricity consumption associated with aeration. This decrease in electricity improves the environmental profile because it entails lower fossil CO2 emissions (Table 4.3). The environmental impacts obtained were transformed into their corresponding environmental costs, which are considered as indirect costs additionally to construction and operational costs (Table 4.4). Scenario 3 presents the worst environmental prices with an increase about 52% in comparison with Scenario 4 and 80% more than Scenarios 1 and 2. The main categories that cause this negative effect are OD and TET. These categories are influenced by indirect chemical consumption emissions where Scenario 3 is worse than the other scenarios considered. Concerning the operational costs, Scenario 1 followed by Scenario 2 are the most advisable due to electricity production is higher than in the other wastewater schemes considered. Therefore, in Scenario 1, where there is no AD unit in the sludge line, the incorporation of UASB shows that it is a good option for treating wastewater and generating electricity. The worst-scenario in terms of operating costs is Scenario 3 due to the consumption of chemicals to improve the AD process. In addition, in this scenario, two units are included to eliminate OM, so electricity consumption is higher than in the other cases. Operating costs increase by 16% compared to the conventional case and by 32% compared to the other innovative schemes. SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 134 Table 4.3. Environmental results of the different wastewater treatment schemes for the impact categories under assessment (FU: 1 kWh of energy produced) Impact Categories S1 S2 S3 S4 CC (kg CO2 eq) 0.75 0.86 3.63 2.06 OD (kg CFC-11 eq) 4.04·10-7 4.72·10-7 1.00·10-5 1.16·10-6 TA (kg SO2 eq) 0.03 0.03 0.02 0.04 EP (kg PO43- eq) 0.07 0.07 0.09 0.20 HT (kg 1,4-DCB eq) 0.01 0.02 0.11 0.06 PMF (kg PM10 eq) 4.06·10-3 4.08·10-3 5.67·10-3 7.27·10-3 TET (kg 1,4-DCB eq) 0.53 0.69 5.21 2.36 FET (kg 1,4-DCB eq) 0.05 0.07 0.12 0.21 MET (kg 1,4-DCB eq) 0.06 0.07 0.15 0.23 WC (m3) 3.20·10-3 4.20·10-3 0.03 0.01 In terms of construction costs, the most unfavourable scenario is Scenario 3 because there is an extra unit in comparison with the other scenarios followed by Scenarios 1 and 2. Although energy production is higher in these scenarios, the technology is more complex than in the conventional scenarios. For this reason, also depreciation costs are lower in the conventional scenario. The integrated analysis of environmental, operational and construction costs show that Scenario 3 is the worstcase, about 51% more than conventional and when compared with innovative schemes the difference increased up to 87% and 85% in Scenarios 1 and 2, respectively. CHAPTER 4: PURSING ENERGY SELF-SUFFICIENT IN WASTEWATER TREATMENTS PLANTS: ENVIRONMENTAL AND ECONOMIC ASSESSMENT OF INNOVATIVE OPTIONS 135 Table 4.4. Operational and construction costs of the different wastewater schemes considered (FU: 1 kWh of energy produced) Costs S1 S2 S3 S4 Operational costs Electricity 0.12 0.17 0.23 0.36 Chemical consumption 3.31·10-4 3.31·10-4 0.35 6.30·10-4 Sludge management 9.87·10-3 9.77·10-3 9.84·10-3 1.64·10-2 Staff 0.15 0.15 0.16 0.28 Lab. costs 3.91·10-3 3.91·10-3 4.37·10-3 7.43·10-3 Maintenance 0.09 0.09 0.10 0.18 Other costs 0.03 0.03 0.04 0.06 TOTAL OPEX (€) 0.40 0.45 0.89 0.90 Construction costs Pre-treatment 3.24·10-3 3.24·10-3 3.62·10-3 6.16·10-3 UASB 7.57·10-3 - - - HRAS - 2.51·10-3 - - CEPT - - 4.68·10-3 - RBF - - 2.08·10-2 - PC - - - 1.70·10-2 Cogeneration unit 1.33·10-3 1.33·10-3 1.48·10-3 2.52.10-3 IFAS 0.28 0.28 0.31 - CAS - - - 0.09 Thickening 1.16·10-3 1.16·10-3 1.30·10-3 2.21·10-3 AD unit - 7.57·10-3 8.46·10-3 5.66·10-3 Dewatering 5.47·10-3 5.47·10-3 6.12·10-3 0.01 Composting unit 2.98·10-3 2.98·10-3 3.33·10-3 0.01 TOTAL CAPEX (€) 0.30 0.30 0.36 0.14 DEPRECIATION COSTS (€) 0.30 0.31 0.36 0.12 TOTAL INDIRECT COSTS (€) 5.45 6.95 47.81 22.63 TOTAL COSTS (€) 6.45 7.99 49.42 23.79 SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 136 4.3.2. Environmental perspective for each wastewater treatment configuration To better understand the contribution of the impact that each unit that formed the wastewater treatment scheme can create, the environmental impacts are studied individually for each scenario. As in the case before, the results are calculated on the basis of the FU (1 kWh of energy produced). In Scenario 1 (UASB + IFAS), the main contributor to all impact categories except TA and PMF is the IFAS unit. This impact is related to the indirect emissions associated with the electricity consumption for the CC, OF or FD categories. In categories such as EP, TET, FET and MET, the impact is associated with the discharge of the effluent into the environment. The negative effect is related to the presence of heavy metals in the wastewater. Their bioaccumulation potential can affect wildlife and vegetation over time (Figure 4.5a). In TA and PMF categories, the main contributor to the impact is the composting unit. Air emissions associated with this unit are the cause of the impact on this process. The value of these emissions is presented in Table 4.3 (materials and methods section). In the CC category, the impacts are more distributed: 40% IFAS unit, 30% composting unit and 24% UASB unit. The impact of the UASB unit is related to the atmospheric emissions of CH4, H2S and CO2 (Table 4.3; material and methods section). However, the UASB impact is very small and even negligible in some categories such as FET, MET or TA. Finally, the impacts of the other units such as dewatering or cogeneration can be considered non-significant (Figure 4.5a). The results for Scenario 2 (HRAS + IFAS) are shown in Figure 4.5.b. As in the previous scenario, the main contributor to the impact in all categories except TA and PMF is the IFAS unit. As explained above, the impact is associated with the direct emissions related to the effluent discharge and the indirect emissions associated to the electricity consumption in this unit. In this case, the AD unit represents a negative effect between 3% in FET category and 30% in CC category, which is mainly attributed to biogas losses (Table 4.3; materials and methods section). The composting unit is the main contributor to the negative effect on TA and PMF (as in Scenario 1) and the effect is caused by the air CHAPTER 4: PURSING ENERGY SELF-SUFFICIENT IN WASTEWATER TREATMENTS PLANTS: ENVIRONMENTAL AND ECONOMIC ASSESSMENT OF INNOVATIVE OPTIONS 137 emissions. As for HRAS, which is the new unit in this configuration, the impact ranges from 11% in FD to 1% in the TA category. Finally, the effect of dewatering or thickening unit can be considered negligible (Figure 4.5.b). Figure 4.5.c shows the contribution per subsystem in Scenario 3 (RBF + CEPT + IFAS). In this scenario, the results change (Table 4.3). The CEPT unit is the main contributor to the impact in all categories except TA, CC and EP. This is due to the amount of chemicals used to achieved greater OM recovery. The impacts are associated with indirect emissions related to the production of the chemical used in this process (FeCl3). In the TA category, air emissions caused in the composting unit are the main factor contributing to the negative effect (53%). In the EP category (as in the previous scenarios), the discharge of the effluent into the aquatic environment is detrimental for the environmental score. In the RBF, which is the new unit in this configuration, the main impact ranges from 13% in the OD category to 5% in the MET category. In CC, the AD unit contributes around 46% of the total impact, followed by the CEPT unit. Finally, other units such as dewatering, thickening or pre-treatment have an impact that can be considered non-significant. Finally, Figure 4.5.d presents the results for the conventional scenario (PC + CAS with nitrogen removal). The activated sludge reactor is the worst unit in terms of environmental impact in all categories except TA and PMF. The negative effect of this unit is associated with the high electricity consumption and the direct emissions when the effluent is discharged into the environment. In the TA and PMF categories, the composting unit is the main contributor to the impact. As in the previous scenarios, the impact is related to the air emissions that occur in this process when the compost is produced. The PC unit has a negligible impact such as dewatering, cogeneration or thickening units. SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 144 4.4.4. Sensitivity analysis of the functional unit (FU) In LCA methodology, a crucial step is the definition of the FU, since this decision influences the inventory data and the results. In this case, maximising electricity production is a key factor in our system. However, the main function of WWTPs is to treat wastewater. In this sense, it is important to evaluate the influence of the selection of the FU on the outcomes of the analysis. Therefore, two FU were studied and compared (1 kWh of energy produced and 1 m3 of treated wastewater). The category studied was the CC category, because this category is the most influenced by possible changes in energy consumption or production (Zouboulis and Tolkou, 2015). Figure 4.7 shows the results of the different scenarios for both FU. These results are very similar and range from 5% in Scenario 3 to 1% in the other scenarios; therefore, the difference is not significant. Thus, the choice of another FU does not change the results and Scenario 1 would be the best from an environmental perspective. Figure 4.7. Comparison between two different functional units (1 m3 of treated wastewater and 1 kWh of energy produced) for the climate change category. Symbols: o represents 1 m3 of treated wastewater; Δ represents 1 kWh of energy produced) CHAPTER 4: PURSING ENERGY SELF-SUFFICIENT IN WASTEWATER TREATMENTS PLANTS: ENVIRONMENTAL AND ECONOMIC ASSESSMENT OF INNOVATIVE OPTIONS 145 4.5. CONCLUSIONS In this study, a new treatment strategy focused on OM recovery was evaluated from an environmental and economic perspective. Three schemes based on this strategy: (i) UASB + IFAS; (ii) HRAS + IFAS, and (iii) RBF + CEPT + IFAS) were compared with a conventional treatment scenario (PC + CAS). The UASB and HRAS followed by an IFAS unit had a better environmental profile than the conventional technology. Moreover, the energy consumption in aeration can decrease by 13% when IFAS is integrated. However, not all schemes based on this strategy showed a better environmental and economic profile. Technologies that require chemical achieved worse results than the conventional system in the ecotoxicity and human health categories. In addition, costs can increase by 51% compared to the conventional plant. When a technology is implemented, validation is needed not only form a technology point of view but also from an environmental and economic perspective. In this way, these elements that are considered end-of-pipe systems for waste treatment can be adapted to the circular economy and become more sustainable. 4.6. REFERENCES Appels, L., Baeyens, J., Degrève, J., Dewil, R., 2008. Principles and potential of the anaerobic digestion of waste-activated sludge. Prog. Energy Combust. Sci. 34, 755–781. https://doi.org/10.1016/j.pecs.2008.06.002 Atandi, E., Rahman, S., 2012. Prospect of anaerobic co-digestion of dairy manure: a review. Environ. Technol. Rev. 1, 127–135. https://doi.org/10.1080/09593330.2012.698654 Barbosa, M.O., Moreira, N.F.F., Ribeiro, A.R., Pereira, M.F.R., Silva, A.M.T., 2016. Occurrence and removal of organic micropollutants: An overview of the watch list of EU Decision 2015/495. Water Res. 94, 257–279. https://doi.org/10.1016/j.watres.2016.02.047 Bdour, A.N., Hamdi, M.R., Tarawneh, Z., 2009. Perspectives on sustainable wastewater treatment technologies and reuse options in the urban areas of the Mediterranean region. Desalination 237, 162–174. https://doi.org/10.1016/j.desal.2007.12.030 SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 146 Bertanza, G., Baroni, P., Canato, M., 2016. Ranking sewage sludge management strategies by means of Decision Support Systems: A case study. Resour. Conserv. Recycl. 110, 1–15. https://doi.org/10.1016/j.resconrec.2016.03.011 Bertanza, G., Canato, M., Laera, G., Vaccari, M., Svanström, M., Heimersson, S., 2017. A comparison between two full-scale MBR and CAS municipal wastewater treatment plants: techno-economic-environmental assessment. Environ. Sci. Pollut. Res. 24, 17383–17393. https://doi.org/10.1007/s11356-017-9409-3 Boldrin, A., Andersen, J.K., Møller, J., Christensen, T.H., Favoino, E., 2009. Composting and compost utilization: Accounting of greenhouse gases and global warming contributions. Waste Manag. Res. 27, 800–812. https://doi.org/10.1177/0734242X09345275 Braguglia, C.M., Gianico, A., Gallipoli, A., Mininni, G., 2015. The impact of sludge pre-treatments on mesophilic and thermophilic anaerobic digestion efficiency: Role of the organic load. Chem. Eng. J. 270, 362–371. https://doi.org/10.1016/j.cej.2015.02.037 Cano, R., Pérez-Elvira, S., Fernádez-Polanco, F., 2015. Energy feasibility study of sludge pretreatments : A review. Appl. Energy 149, 176–185. https://doi.org/10.1016/j.apenergy.2015.03.132 Cieslik, B.M., Namiesnik, J., Konieczka, P., 2015. Review of sewage sludge management: Standards, regulations and analytical methods. J. Clean. Prod. 90, 1–15. https://doi.org/10.1016/j.jclepro.2014.11.031 De Bruyn, S., Bijleveld, M., de Graaff, L., Schep, E., Schroten, A., Vergeer, R., Ahdour, S., 2018. Environmental Prices Handbook EU28 Version. CE Delft 175. Dones R., Bauer C., Bolliger R., Burger B., Faist Emmenegger M., Frischknecht R., Heck T., Jungbluth N., Röder A., T.M., 2007. Life cycle inventories of energy systems: results of current systems in Switzerland and other UCTE countries. Ecoinvent Rep.5. https://doi.org/10.1007/s11367-014-0838-7 Garrido-Baserba, M., Hospido, A., Reif, R., Molinos-Senante, M., Comas, J., Poch, M., 2014. Including the environmental criteria when selecting a wastewater treatment plant. Environ. Model. Softw. 56, 74–82. https://doi.org/10.1016/j.envsoft.2013.11.008 CHAPTER 4: PURSING ENERGY SELF-SUFFICIENT IN WASTEWATER TREATMENTS PLANTS: ENVIRONMENTAL AND ECONOMIC ASSESSMENT OF INNOVATIVE OPTIONS 147 Garrido-Baserba, M., Molinos-Senante, M., Abelleira-Pereira, J.M., Fdez-Güelfo, L.A., Poch, M., Hernández-Sancho, F., 2015. Selecting sewage sludge treatment alternatives in modern wastewater treatment plants using environmental decision support systems. J. Clean. Prod. 107, 410–419. https://doi.org/10.1016/j.jclepro.2014.11.021 Gikas, P., 2017. Towards energy positive wastewater treatment plants. J. Environ. Manage. 203, 621–629. https://doi.org/10.1016/j.jenvman.2016.05.061 Godin, D., Bouchard, C., Vanrolleghem, P.A., 2012. Net environmental benefit: Introducing a new LCA approach on wastewater treatment systems. Water Sci. Technol. 65, 1624–1631. https://doi.org/10.2166/wst.2012.056 Gu, J., Yang, Q., Liu, Y., 2018. Mainstream anammox in a novel A-2B process for energy-efficient municipal wastewater treatment with minimized sludge production. Water Res. 138, 1–6. https://doi.org/10.1016/j.watres.2018.02.051 Guinée, J., 2002. Handbook on Life Cycle Assessment Operational Guide to the ISO Standards. Environ. Impact Assess. Rev. 23, 129–130. https://doi.org/10.1016/S0195-9255(02)00101-4 Hijazi, O., Munro, S., Zerhusen, B., Effenberger, M., 2016. Review of life cycle assessment for biogas production in Europe. Renew. Sustain. Energy Rev. 54, 1291–1300. https://doi.org/10.1016/j.rser.2015.10.013 Hospido, A., Moreira, M.T., Fernández-Couto, M., Feijoo, G., 2004. Environmental performance of a municipal wastewater treatment plant. Int. J. Life Cycle Assess. 9, 261–271. https://doi.org/10.1007/BF02978602 Houtmeyers, S., Degrève, J., Willems, K., Dewil, R., Appels, L., 2014. Comparing the influence of low power ultrasonic and microwave pre-treatments on the solubilisation and semi-continuous anaerobic digestion of waste activated sludge. Bioresour. Technol. 171, 44–49. https://doi.org/10.1016/j.biortech.2014.08.029 Huijbregts, M.A.J., Steinmann, Z.J.N., Elshout, P.M.F., Stam, G., Verones, F., Vieira, M.D.M., Hollander, A., Zijp, M., van Zelm, R., 2017. ReCiPe 2016 v1.1. Jimenez, J., Miller, M., Bott, C., Murthy, S., De Clippeleir, H., Wett, B., 2015. Highrate activated sludge system for carbon management - Evaluation of crucial process mechanisms and design parameters. Water Res. 87, 476–482. https://doi.org/10.1016/j.watres.2015.07.032 SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 148 Kacprzak, M., Neczaj, E., Fijałkowski, K., Grobelak, A., Grosser, A., Worwag, M., Rorat, A., Brattebo, H., Almås, Å., Singh, B.R., 2017. Sewage sludge disposal strategies for sustainable development. Environ. Res. 156, 39–46. https://doi.org/10.1016/j.envres.2017.03.010 Kelessidis, A., Stasinakis, A.S., 2012. Comparative study of the methods used for treatment and final disposal of sewage sludge in European countries. Waste Manag. 32, 1186–1195. https://doi.org/10.1016/j.wasman.2012.01.012 Komesli, O.T., Teschner, K., Hegemann, W., Gokcay, C.F., 2007. Vacuum membrane applications in domestic wastewater reuse. Desalination 215, 22–28. https://doi.org/10.1016/j.desal.2006.10.025 Lehtoranta, S., Vilpas, R., Mattila, T.J., 2014. Comparison of carbon footprints and eutrophication impacts of rural on-site wastewater treatment plants in Finland. J. Clean. Prod. 65, 439–446. https://doi.org/10.1016/j.jclepro.2013.08.024 Lorenzo-Toja, Y., Alfonsín, C., Amores, M.J., Aldea, X., Marin, D., Moreira, M.T., Feijoo, G., 2016a. Beyond the conventional life cycle inventory in wastewater treatment plants. Sci. Total Environ. 553, 71–82. https://doi.org/10.1016/j.scitotenv.2016.02.073 Lorenzo-Toja, Y., Vázquez-Rowe, I., Amores, M.J., Termes-Rifé, M., Marín- Navarro, D., Moreira, M.T., Feijoo, G., 2016b. Benchmarking wastewater treatment plants under an eco-efficiency perspective. Sci. Total Environ. 566–567, 468–479. https://doi.org/10.1016/j.scitotenv.2016.05.110 Lotti, T., Kleerebezem, R., Hu, Z., Kartal, B., Kreuk, M.K. De, Taalman, C.V.E., Kruit, J., Hendrickx, T.L.G., Loosdrecht, M.C.M. Van, Kleerebezem, R., Hu, Z., Kartal, B., Kreuk, M.K. De, Taalman, C.V.E., 2015. Pilot-scale evaluation of anammox-based mainstream nitrogen removal from municipal wastewater 3330. https://doi.org/10.1080/09593330.2014.982722 Luostarinen, S., Luste, S., Sillanpää, M., 2009. Increased biogas production at wastewater treatment plants through co-digestion of sewage sludge with grease trap sludge from a meat processing plant. Bioresour. Technol. 100, 79–85. https://doi.org/10.1016/j.biortech.2008.06.029 Ma, J., Duong, T.H., Smits, M., Verstraete, W., Carballa, M., 2011. Enhanced biomethanation of kitchen waste by different pre-treatments. Bioresour. Technol. 102, 592–599. https://doi.org/10.1016/j.biortech.2010.07.122 CHAPTER 4: PURSING ENERGY SELF-SUFFICIENT IN WASTEWATER TREATMENTS PLANTS: ENVIRONMENTAL AND ECONOMIC ASSESSMENT OF INNOVATIVE OPTIONS 149 Malovanyy, A., Trela, J., Plaza, E., 2015. Mainstream wastewater treatment in integrated fixed film activated sludge (IFAS) reactor by partial nitritation/anammox process. Bioresour. Technol. 198, 478–487. https://doi.org/10.1016/j.biortech.2015.08.123 Mata-Alvarez, J., Dosta, J., Romero-Güiza, M.S., Fonoll, X., Peces, M., Astals, S., 2014. A critical review on anaerobic co-digestion achievements between 2010 and 2013. Renew. Sustain. Energy Rev. 36, 412–427. https://doi.org/10.1016/j.rser.2014.04.039 Morales, N., Val del Río, Á., Vázquez-Padín, J.R., Méndez, R., Mosquera-Corral, A., Campos, J.L., 2015. Integration of the Anammox process to the rejection water and main stream lines of WWTPs. Chemosphere 140, 99–105. https://doi.org/10.1016/j.chemosphere.2015.03.058 Mu’Azu, N.D., Essa, M.H., Aga, O., Jarrah, N., 2019. Life cycle assessment approach to sustainable sewage sludge management for water pollution control. J. Phys. Conf. Ser. 1349. https://doi.org/10.1088/1742- 6596/1349/1/012145 Neumann, P., Pesante, S., Venegas, M., Vidal, G., 2016. Developments in pretreatment methods to improve anaerobic digestion of sewage sludge. Rev. Environ. Sci. Biotechnol. 15, 173–211. https://doi.org/10.1007/s11157- 016-9396-8 Petit-Boix, A., Sanjuan-Delmás, D., Gasol, C.M., Villalba, G., Suárez-Ojeda, M.E., Gabarrell, X., Josa, A., Rieradevall, J., 2014. Environmental Assessment of Sewer Construction in Small to Medium Sized Cities Using Life Cycle Assessment. Water Resour. Manag. 28, 979–997. https://doi.org/10.1007/s11269-014-0528-z Piao, W., Kim, Y., Kim, H., Kim, M., Kim, C., 2016. Life cycle assessment and economic efficiency analysis of integrated management of wastewater treatment plants. J. Clean. Prod. 113, 325–337. https://doi.org/10.1016/j.jclepro.2015.11.012 Pradel, M., Aissani, L., 2019. Environmental impacts of phosphorus recovery from a “product” Life Cycle Assessment perspective: Allocating burdens of wastewater treatment in the production of sludge-based phosphate fertilizers. Sci. Total Environ. 656, 55–69. https://doi.org/10.1016/j.scitotenv.2018.11.356 Raheem, A., Sikarwar, V.S., He, J., Dastyar, W., Dionysiou, D.D., Wang, W., Zhao, M., 2018. Opportunities and challenges in sustainable treatment and resource reuse of sewage sludge: A review. Chem. Eng. J. 337, 616–641. https://doi.org/10.1016/j.cej.2017.12.149 SECTION I: IMPROVING CENTRALISED WASTEWATER SYSTEMS 150 Rashidi, J., Rhee, G.H., Kim, M., Nam, K.J., Heo, S., Yoo, C.K., Karbassi, A., 2018. Life Cycle and Economic Assessments of Key Emerging Energy Efficient Wastewater Treatment Processes for Climate Change Adaptation. Int. J. Environ. Res. 12, 815–827. https://doi.org/10.1007/s41742-018-0135-6 REE, 2018. Spanish Power Systems 2018.Annual report Rodriguez-Garcia, G., Molinos-Senante, M., Hospido, A., Hernández-Sancho, F., Moreira, M.T., Feijoo, G., 2011. Environmental and economic profile of six typologies of wastewater treatment plants. Water Res. 45, 5997–6010. https://doi.org/10.1016/j.watres.2011.08.053 Ruiken, C.J., Breuer, G., Klaversma, E., Santiago, T., Loosdrecht, M.C.M. Van, 2012. Sieving wastewater e Cellulose recovery , economic and energy evaluation. Water Res. 47, 43–48. https://doi.org/10.1016/j.watres.2012.08.023 Schindler, D.W., 2010. Recent advances in the understanding and management of eutrophication. Limnol. Oceanogr. 51, 356–363. https://doi.org/10.4319/lo.2006.51.1_part_2.0356 Stocker, T.F., Qin, D., Plattner, G.K., Tignor, M., Allen, S.K., Boschung, J., Nauels, A., Xia, Y., Bex, B., Midgley, B.M., 2013. IPCC, 2013: Summary for Policymakers. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Tchobanoglous, G., Burton, F., Stensel, H.D., 1998. Wastewater engineering: An Overview, in: Wastewater Engineering Treatment and Reuse. pp. 1–24. https://doi.org/10.1016/0309-1708(80)90067-6 Tomei, M.C., Bertanza, G., Canato, M., Heimersson, S., Laera, G., Svanström, M., 2016. Techno-economic and environmental assessment of upgrading alternatives for sludge stabilization in municipal wastewater treatment plants. J. Clean. Prod. 112, 3106–3115. https://doi.org/10.1016/j.jclepro.2015.10.017 Van Dongen, U., Jetten, M.S.M., Van Loosdrecht, M.C.M., 2001. The SHARON®- Anammox® process for treatment of ammonium rich wastewater. Water Sci. Technol. 44, 153–160. Vázquez-Padín, J., Mosquera-Corral, A., Campos, J.L., Méndez, R., Revsbech, N.P., 2010. Microbial community distribution and activity dynamics of granular biomass in a CANON reactor. Water Res. 44, 4359–4370. https://doi.org/10.1016/j.watres.2010.05.041 CHAPTER 4: PURSING ENERGY SELF-SUFFICIENT IN WASTEWATER TREATMENTS PLANTS: ENVIRONMENTAL AND ECONOMIC ASSESSMENT OF INNOVATIVE OPTIONS 151 Wan, J., Gu, J., Zhao, Q., Liu, Y., 2016. OPEN COD capture : a feasible option towards energy self-sufficient domestic wastewater treatment. Nat. Publ. Gr. 1–9. https://doi.org/10.1038/srep25054 Wang, M., Sun, X., Li, P., Yin, L., Liu, D., Zhang, Y., Li, W., Zheng, G., 2014. A novel alternate feeding mode for semi-continuous anaerobic co-digestion of food waste with chicken manure. Bioresour. Technol. 164, 309–314. https://doi.org/10.1016/j.biortech.2014.04.077 Wernet, G., Bauer, C., Steubing, B., Reinhard, J., Moreno-Ruiz, E., Weidema, B., 2016. The ecoinvent database version 3 (part I): overview and methodology. Int. J. Life Cycle Assess. 21, 1218–1230. https://doi.org/10.1007/s11367-016-1087-8 Xu, G., Zhou, Y., Yang, Q., Lee, Z.M.P., Gu, J., Lay, W., Cao, Y., Liu, Y., 2015. The challenges of mainstream deammonification process for municipal used water treatment. Appl. Microbiol. Biotechnol. 99, 2485–2490. https://doi.org/10.1007/s00253-015-6423-6 Yang, Y., Zhang, L., Cheng, J., Zhang, S., Li, B., Peng, Y., 2017. Achieve efficient nitrogen removal from real sewage in a plug-flow integrated fixed-film activated sludge (IFAS) reactor via partial nitritation/anammox pathway. Bioresour. Technol. 239, 294–301. https://doi.org/10.1016/j.biortech.2017.05.041 Zouboulis, A., Tolkou, A., 2015. Effect of Climate Change in Wastewater Treatment Plants: Reviewing the Problems and Solutions, in: Shrestha, S., Anal, A.K., Salam, P.A., van der Valk, M. (Eds.), Managing Water Resources under Climate Uncertainty: Examples from Asia, Europe, Latin America, and Australia. Springer International Publishing, Cham, pp. 197–220. https://doi.org/10.1007/978-3-319-10467-6_10 Andrea Arias*a, Chitta Rajan Beherab, Gumersindo Feijooa, Gürkan Sinb, María Teresa Moreiraa. “Unravelling the environmental and economic impacts of innovative technologies for the enhancement of biogas production and sludge management in wastewater systems”. Journal of Environmental Management. 2020, Vol. 227, 110965. https://doi.org/10.1016/j.jenvman.2020.110965. aCRETUS institute. Department of Chemical Engineering. Universidade de Santiago de Compostela, E-15782, Santiago de Compostela, Galicia, Spain. b Process and Systems Engineering Center (PROSYS), Department of Chemical and Biochemical Engineering, Technical University of Denmark, Building 229, 2800 Kgs. Lyngby, Denmark CHAPTER 5: Mapping the environmental and economic impacts of innovative technologies for enhancement of biogas production and sludge management in wastewater systems SUMMARY In recent years, new wastewater treatment plans have been proposed to tackle more complex challenges. To address these new configurations, it is necessary to use tools to model, optimise and select the most appropriate plant layout for each scenario. It is not possible to embark on the construction of new facilities unless the previous technical, economic and environmental feasibility studies have been rigorously considered. It is well known that the elements that penalise the wastewater treatment are: i) energy consumption and ii) sludge management. Based on these premises, the main objective of Chapter 5 is to evaluate which treatment configuration ensures the efficient water-energy nexus and the reduction of the operational costs linked to the wastewater scheme. For this purpose, the treatment configuration of two real plants of different size was modified to include some novel concepts such as physicalchemical and biological processes for the recovery of organic matter OM in the primary treatment, as well as the implementation of a partial nitrification-anammox process in the secondary treatment. According to the modelling results that integrate the environmental and economic indicators using the LCA methodology, the schemes based on HRAS or RBF + chemical addition followed a partial nitrification-Anammox led to the best environmental and economic results. These results are attributed to increased biogas production and reduced electricity demand from the grid. Furthermore, these schemes proved to be costeffective and environmental-friendly for both plant sizes and configurations. SECTION II: CHANGING THE PARADIGM OF WASTEWATER TREATMENT 256 Figure 8.2. Decentralised neighbourhood scheme: a) general configuration; b) System boundaries for Scenario 3 (decentralised system with conventional toilets); c) System boundaries for Scenario 4 (decentralised system with vacuum toilets) 8.2.2. Life cycle inventory (LCI) for the different wastewater treatment configurations The inventories were made with primary data (real data) and secondary data (calculated or bibliographic data), reported in Tables 8.1 and 8.2. The primary data correspond with the real data which are associated with the centralised case. The characteristics of the wastewater, the amount of sludge generated and the consumption of chemicals were obtained from an internal report (PRTR, 2017). Moreover, electricity consumption and biogas production (Scenario 2) b) c) CHAPTER 8. ENVIRONMENTAL ANALYSIS OF SERVICING CENTRALISED AND DECENTRALISED WASTEWATER TREATMENT FOR POPULATION LIVING IN NEIGHBOURHOODS 257 were obtained using estimated data. In the decentralised cases, the data are obtained through bibliographic information and mass balances. BW, GW, biogas transformation or energy consumption are bibliographical data (Komesli et al., 2007; Zang et al., 2015; Zeeman et al., 2008). Therefore, the inventories were completed with the Ecoinvent v3.5 database (Wernet et al., 2016). Finally, several simplifications were made for background data. Electricity: Spanish electricity country mix was updated for the 2018 year with the data form the annual report (REE, 2018). As regards the consumption of chemical products, polyelectrolyte was implemented as cationic resin taking into account the Ecoinvent v3.5 database (Wernet et al., 2016). Biogas composition was considered such as 75% CH4, 24% CO2 and 1% H2S (Kujawa-Roeleveld et al., 2006). Finally, the emissions of composting to air (CH4, CO2, N2O and NH3) were estimated through bibliographic data (Boldrin et al., 2009). SECTION II: CHANGING THE PARADIGM OF WASTEWATER TREATMENT 258 Table 8.1. Main inputs to the different scenarios considered in this study. FU: 1 resident. S1: Scenario 1, S2: Scenario 2, S3: Scenario 3, and S4: Scenario 4 S1 S2 S3 S4 Inputs from the technosphere Materials and fuel Influent COD (g) BW (g) 42.35 42.35 101.3 101.3 GW (g) 53.13 53.13 TN (g) BW (g) 1.31 1.31 175 175 GW (g) 2.15 2.15 TP (g) BW (g) 0.51 0.51 21.87 21.87 GW (g) 0.72 0.72 Electricity consumption Pre-treatment (kWh) 1.57·10-3 1.57·10-3 - - Coagulation-flocculation (kWh) 5.15·10-3 5.15·10-3 - - CAS (kWh) 4.03·10-2 4.03·10-2 - - Thickening + homogenization (kWh) 2.27·10-4 2.27·10-4 - - AD (kWh) - 2.91·10-3 - - Dewatering (kWh) 2.27·10-3 2.27·10-3 - - Composting (kWh) 2.40·10-4 2.40·10-4 - - Toilets (kWh) - - - 0.06 UASB (kWh) - - 3.76·10-3 0.01 MBR (kWh) - - 0.15 0.15 SBR (kWh) - - 0.10 0.10 CHAPTER 8. ENVIRONMENTAL ANALYSIS OF SERVICING CENTRALISED AND DECENTRALISED WASTEWATER TREATMENT FOR POPULATION LIVING IN NEIGHBOURHOODS 259 Table 8.1.(cont.). Main inputs to the different scenarios considered in this study. FU: 1 resident. S1: Scenario 1, S2: Scenario 2, S3: Scenario 3, and S4: Scenario 4 S1 S2 S3 S4 Inputs from the technosphere Chemical consumption - Coagulation-flocculation FeCl3 (kg) 1.93·10-3 1.93·10-3 - - Thickening + homogenization Polyelectrolyte (kg) 4.51·10-2 4.51·10-2 - - Transport FeCl3 (kg·km) 0.05 0.05 - - Polyelectrolyte (kg·km) 1.13 1.13 - - Sludge (kg·km) 0.96 0.96 - - Land application Agricultural machinery (kg) 0.04 0.04 - - SECTION II: CHANGING THE PARADIGM OF WASTEWATER TREATMENT 260 Table 8.2. Main outputs to the different scenarios considered in this study. FU: 1 resident S1 S2 S3 S4 Outputs to the environment Emissions to air AD unit CH4 (kg) - 4.67·10-4 1.06·10-2 1.26·10-2 CO2 (kg) - 5.48·10-4 1.05·10-2 1.25·10-2 H2S (kg) - 9.67·10-6 2.20·10-4 2.60·10-4 Composting unit CH4 (mg) 4.68·10-4 4.68·10-4 - - CO2 (mg) 0.13 0.13 - - N2O (mg) 2.25·10-4 2.25·10-4 - - NH3 (mg) 1.87·10-2 1.87·10-2 - - Land application N2O (kg) 1.33·10-3 1.33·10-3 - - NH3 (kg) 1.09·10-3 1.09·10-3 - - Emissions to water NO-3 (kg) 0.02 0.02 - - PO4-3 (kg) 1.72·10-3 1.72·10-3 - - Outputs to the technosphere Cogeneration unit Electricity production (kWh) - 0.01 0.28 0.33 Heat production (kWh) - 0.01 0.25 0.29 Water for irrigation (m3) - - 0.01 0.01 8.2.3. Indicators for evaluating environmental and economic profile The inventory data were implemented in the SimaPro 9.0 software to obtain the most representative impacts to the different configurations. In this case, the most representative categories are CC due to electricity production and consumption that can affect the reduction or increase of the resident carbon footprint. The other relevant category in this study is WC. As mentioned above, water is used for irrigation. In the centralised case, this water comes from the tap water network, so this tap water has CHAPTER 8. ENVIRONMENTAL ANALYSIS OF SERVICING CENTRALISED AND DECENTRALISED WASTEWATER TREATMENT FOR POPULATION LIVING IN NEIGHBOURHOODS 261 environmental impacts, while in the decentralised case, the water comes from the WWTP. Therefore, it is important to know how this change affects the environmental impacts associated with the residents living in the neighbourhood. These two impact categories were calculated using the ReCiPe Midpoint (H) method (Huijbregts et al., 2017). In addition, for the CC category, the environmental impacts are transformed into environmental prices to obtain how much it would cost to implement these systems from an environmental perspective. The main reason for calculating only the environmental prices in the CC category is because of WC category does not have characterisation factor in this methodology (De Bruyn et al., 2018). Operational and capital costs were calculated as direct economic indicators, whereas environmental prices were quantified such as indirect economic indicators. Operating costs were associated with sludge management, chemical and energy consumption, while capital costs considered only the construction of the unit and incorporated into the total value of WWTP. 8.3. RESULTS AND DISCUSSION 8.3.1. Carbon footprint for each resident according to the different wastewater scheme Environmental impacts were only assessed for the CC and WC categories. In this first section, environmental impacts will be studied for the CC category. For this reason, it is important to know how much energy and water is consumed per resident in each house. In Spain, energy and heat that is consumed per inhabitant is about 1.581 kWh and 425 kWh in a year (IGE, 2016). The biogas produced in the anaerobic digestion units can be used to supply energy and heat to the houses. In this way, the reduction of the carbon footprint per resident can be estimated. The results of the resident´s carbon footprint, depending on the wastewater treatment configuration (centralised or decentralised) are shown in Figure 8.3. The worst values in terms of heat and electricity are SECTION II: CHANGING THE PARADIGM OF WASTEWATER TREATMENT 262 presented for Scenario 1 (centralised case) because there is no AD unit; therefore, there is no generation of these products. Furthermore, when the AD unit is incorporated into the centralised system, the carbon footprint can only be reduced by about 4% in terms of heat and energy. Decentralised cases show better results in reducing the carbon footprint because the production of energy and heat is higher than in centralised systems. The best case is when vacuum toilets are incorporated (Scenario 4) and the reduction is 23% for electricity consumption and 66% for heat production. In Scenario 3 (conventional toilets), the increase is also significant, about 20% for energy and 54% for heat. Thus, these decentralised systems help to decrease the carbon footprint of a resident living in a decentralised wastewater treatment system. Figure 8.3. Carbon footprint in terms of energy and heat for a resident that lives in a centralised or decentralised wastewater scheme. Scenario 1: conventional system, Scenario 2: conventional system with AD unit; Scenario 3: decentralised system with conventional toilets; Scenario 4: decentralised system with vacuum toilets In the context of reducing the carbon footprint, it is also important to study the environmental impacts in the CC category for each wastewater treatment scheme. The different wastewater treatment schemes were 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Scenario 1 Scenario 2 Scenario 3 Scenario 4 CC [kg CO2eq/resident] CHAPTER 8. ENVIRONMENTAL ANALYSIS OF SERVICING CENTRALISED AND DECENTRALISED WASTEWATER TREATMENT FOR POPULATION LIVING IN NEIGHBOURHOODS 263 compared and, in addition, the main impacts for each scheme were analysed. As in the previous analysis, the centralised cases are the worst options because there is no electricity production (Figure 8.4a). In addition, in terms of CC impacts, Scenario 3 (conventional toilets) is the best scenario, even better than Scenario 4 (vacuum toilets). Energy production is higher in Scenario 4 (about 16% than in Scenario 3), however, the energy consumption of the vacuum toilets implies undesirable impacts. Although, the energy consumption is higher than in Scenario 4, the impacts are better than in the conventional systems. If the subsystems of each system in this category are studied, the main impact is the thickening + homogenisation followed by the CAS unit in centralised systems. In the first unit, the impact is associated with the consumption of polyelectrolyte to ensure good sludge dewatering, while in the CAS unit, the negative effect is related to the consumption of energy for aeration. Moreover, the AD incorporation in Scenario 2 does not represent a significant increase in the impact. In decentralised systems, MBR followed by the SBR represent the worst environmental profile due to the energy consumption associated with these units. In addition, the vacuum toilets also have a negative effect of about 10% of the total impact. However, electricity production minimises the total impact of these systems with environmental credits of around 50% in both systems (Figure 8.4b). SECTION II: CHANGING THE PARADIGM OF WASTEWATER TREATMENT 264 Figure 8.4. Environmental impacts for CC category for each resident and environmental impacts for each sub-system that conforms the different wastewater treatment schemes. Scenario 1: conventional system; Scenario 2: conventional system with AD unit; Scenario 3: decentralised system with conventional toilets; Scenario 4: decentralised system with vacuum toilets 8.3.2. Water consumption and reduction for the different wastewater treatment schemes In this section, the reduction in the water consumption was evaluated according to the different wastewater treatment configurations. In Santiago de Compostela, the water used for irrigation is 11.10 m3/inhabitant·year (IGE, 2016). Thus, as in the CC category, the water necessary for irrigation was compared among the different wastewater configurations per inhabitant, in addition, the WC category CHAPTER 8. ENVIRONMENTAL ANALYSIS OF SERVICING CENTRALISED AND DECENTRALISED WASTEWATER TREATMENT FOR POPULATION LIVING IN NEIGHBOURHOODS 265 and the sub-systems affecting to this category were analysed and compared. The total water used in irrigation in this city is 6663 m3/d. This number includes the irrigation of parks, green areas and the provision of water for the fire stations. The neighbourhood studied requires 216 m3/d of irrigation water. In both centralised systems, this number does not decrease because the water in these systems is discharged into the environment. However, in the decentralised cases, water is reused for irrigation. The wastewater generated in Scenario 3 (conventional toilets) is about 788 m3/d because these toilets consume more water than vacuum toilets (Scenario 4), in which the wastewater flow is about 663 m3/d. This means 100% savings in both systems. Therefore, the environmental impacts of tap water treatment would be avoided. For the irrigation of green areas only 216 m3/d of water is required, this means that there is an excess of water of about 572 m3/d (conventional toilets) and 418 m3/d (vacuum toilets) that could be used in other situations, for example, cargo trucks for street cleaning, firefighting, among others. Thus, in the case of decentralised systems, it is not necessary to purify the tap water for irrigation, which means that only the impacts of the irrigation process itself will be taken into account. However, in centralised cases there is no water recovery, so in Scenarios 1 and 2 the impacts of irrigation are associated with the treatment of drinking water. If the irrigation process is analysed for the different scenarios, the environmental results for the WC category show that in the case of centralised systems the impact values are 0.12 m3 of water per resident, while for decentralised cases the negative effect is about 3.03·10-3 m3 of water per resident. These results show an improvement of around 99% in the environmental profile because the production and distribution of tap water that is caused by the centralised configurations involve large environmental impacts. Figure 8.5 shows the main results for the WC category for each wastewater treatment scheme considered. In addition, the subsystems SECTION II: CHANGING THE PARADIGM OF WASTEWATER TREATMENT 272 nutrients. In addition, decentralised systems are characterised by a lower sewage network compared to centralised systems (Opher and Friedler, 2016). It is estimated that the sewer network has an have a significant contribution to the overall impact of construction of WWTPs (Petit-Boix et al., 2014). Thus, in this case, it was evaluated how the sewerage network affects the environmental profile. In the city of Santiago de Compostela, the extension of sewage network is 647 km, which implies an amount of 5 m/inhabitant. In decentralised systems, this figure is estimated to be about 3.7 m/inhabitant (Kjerstadius et al., 2017). If the environmental profiles are compared, as expected, the centralised system (455 kg CO2eq/resident) has 76% higher amount that the decentralised systems (108 kg CO2eq/resident). These impacts are related to the production of concrete for trenching and pipe material but not only these factors are important, there are taken into account the capacity of the sewer network. The sewer network in Santiago de Compostela has a higher capacity because there is no separation network (wastewater and rainwater), therefore, the capacity of the sewerage must be high because in this city the rainfall is high. On the contrary, in the decentralised system, although there are two pipes (one for BW and another for GW), the capacity is reduced. This implies less environmental impacts related to the construction of the pipelines, ditches or even direct emissions related to the construction. The introduction of a separate network in Santiago is not simple due to the protection of its old town, so changing the sewage network is not a viable option, but decentralised systems of wastewater and sewage can be a good alternative in new neighbourhoods and can improve the environmental profile of these networks not only in the CC category but in all categories, making the resident have less consumption of carbon and water in terms of irrigation than residents who choose another type of neighbourhood. CHAPTER 8. ENVIRONMENTAL ANALYSIS OF SERVICING CENTRALISED AND DECENTRALISED WASTEWATER TREATMENT FOR POPULATION LIVING IN NEIGHBOURHOODS 273 8.4. CONCLUSIONS In this Chapter, the carbon footprint and water consumption for irrigation of a resident living in a centralised wastewater district was compared to that of a resident who chooses to live in a decentralised wastewater district. The study was carried out in the city of Santiago de Compostela. In this framework, two centralised configurations: (i) conventional system without AD unit and (ii) a conventional system with the incorporation of AD unit were compared with decentralised options: one with conventional toilets and another with vacuum toilets. The decentralised options show a reduction of the resident carbon footprint by 20-23% due to electricity production. Furthermore, with the reclaimed water, these systems can supply water for irrigation of green areas, so no extra consumption of tap water is required. Although these new systems present more construction costs and are more complex, the recovery time is less than in conventional systems due to the recovery of products such as energy or water. However, the incorporation of these systems is not easier due to the robustness of conventional systems. Thus, the option of decentralised cases can be an optimal solution for new buildings or residential areas. 8.5. REFERENCES Boldrin, A., Andersen, J.K., Møller, J., Christensen, T.H., Favoino, E., 2009. Composting and compost utilization: Accounting of greenhouse gases and global warming contributions. Waste Manag. Res. 27, 800–812. https://doi.org/10.1177/0734242X09345275 De Bruyn, S., Bijleveld, M., de Graaff, L., Schep, E., Schroten, A., Vergeer, R., Ahdour, S., 2018. Environmental Prices Handbook EU28 Version. CE Delft 175. Goldstein, B., Birkved, M., Quitzau, M.B., Hauschild, M., 2013. Quantification of urban metabolism through coupling with the life cycle assessment framework: Concept development and case study. Environ. Res. Lett. 8. https://doi.org/10.1088/1748-9326/8/3/035024 SECTION II: CHANGING THE PARADIGM OF WASTEWATER TREATMENT 274 González-García, S., Dias, A.C., 2019. Integrating lifecycle assessment and urban metabolism at city level: Comparison between Spanish cities. J. Ind. Ecol. 23, 1062–1076. https://doi.org/10.1111/jiec.12844 Huijbregts, M.A.J., Steinmann, Z.J.N., Elshout, P.M.F., Stam, G., Verones, F., Vieira, M.D.M., Hollander, A., Zijp, M., van Zelm, R., 2017. ReCiPe 2016 v1.1. IGE, I.G. de E., 2016. Population Equivalent (in spanish) [WWW Document]. URL https://www.ige.eu/igebdt/selector.jsp?COD=590&paxina=001&c=0201 001002 Kennedy, C., Steinberger, J., Gasson, B., Hansen, Y., Hillman, T., Havránek, M., Pataki, D., Phdungsilp, A., Ramaswami, A., Mendez, G.V., 2009. Greenhouse gas emissions from global cities. Environ. Sci. Technol. 43, 7297–7302. https://doi.org/10.1021/es900213p Kjerstadius, H., Haghighatafshar, S., Davidsson, A., 2015. Potential for nutrient recovery and biogas production from blackwater, food waste and greywater in urban source control systems. Environ. Technol. (United Kingdom) 36, 1707–1720. https://doi.org/10.1080/09593330. 2015.1007089 Kobayashi, Y., Ashbolt, N.J., Davies, E.G.R., Liu, Y., 2020. Life cycle assessment of decentralized greywater treatment systems with reuse at different scales in cold regions. Environ. Int. 134, 105215. https://doi.org/10.1016/ j.envint.2019.105215 Komesli, O.T., Teschner, K., Hegemann, W., Gokcay, C.F., 2007. Vacuum membrane applications in domestic wastewater reuse. Desalination 215, 22–28. https://doi.org/10.1016/j.desal.2006.10.025 Kujawa-Roeleveld, K., Elmitwalli, T., Zeeman, G., 2006. Enhanced primary treatment of concentrated black water and kitchen residues within DESAR concept using two types of anaerobic digesters. Water Sci. Technol. 53, 159–168. https://doi.org/10.2166/wst.2006.265 Lahmouri, M., Drewes, J.E., Gondhalekar, D., 2019. Analysis of greenhouse gas emissions in centralized and decentralizedwater reclamation with resource recovery strategies in Leh Town, Ladakh, India, and potential for their reduction in context of the Water-Energy-Food Nexus. Water (Switzerland) 11. https://doi.org/10.3390/w11050906 CHAPTER 8. ENVIRONMENTAL ANALYSIS OF SERVICING CENTRALISED AND DECENTRALISED WASTEWATER TREATMENT FOR POPULATION LIVING IN NEIGHBOURHOODS 275 Opher, T., Friedler, E., 2016. Comparative LCA of decentralized wastewater treatment alternatives for non-potable urban reuse. J. Environ. Manage. 182, 464–476. https://doi.org/10.1016/j.jenvman.2016.07.080 Petit-Boix, A., Sanjuan-Delmás, D., Gasol, C.M., Villalba, G., Suárez-Ojeda, M.E., Gabarrell, X., Josa, A., Rieradevall, J., 2014. Environmental Assessment of Sewer Construction in Small to Medium Sized Cities Using Life Cycle Assessment. Water Resour. Manag. 28, 979–997. https://doi.org/10.1007/ s11269-014-0528-z PRTR, 2017. Registro Estatal de Emisiones y Fuentes Contaminantes. Madrid. REE, 2018. Spanish Power Systems 2018. Annual report Samuel, S., Lim, M., Hsien, C., Ho, A., Schraudolph, U., White, S., 2016. Blue buildings: Decentralized and integrated management of water from ‘source-to-source, at source.’ Water Pract. Technol. 11, 601–609. https://doi.org/10.2166/wpt.2016.065 Shen, Y., Linville, J.L., Urgun-Demirtas, M., Mintz, M.M., Snyder, S.W., 2015. An overview of biogas production and utilization at full-scale wastewater treatment plants (WWTPs) in the United States: Challenges and opportunities towards energy-neutral WWTPs. Renew. Sustain. Energy Rev. 50, 346–362. https://doi.org/10.1016/j.rser.2015.04.129 Steffen, W., Broadgate, W., Deutsch, L., Gaffney, O., Ludwig, C., 2015. The trajectory of the anthropocene: The great acceleration. Anthr. Rev. 2, 81– 98. https://doi.org/10.1177/2053019614564785 Stocker, T.F., Qin, D., Plattner, G.K., Tignor, M., Allen, S.K., Boschung, J., Nauels, A., Xia, Y., Bex, B., Midgley, B.M., 2013. IPCC, 2013: Summary for Policymakers. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. United Nations, 2015. Transforming our world: the 2030 Agenda for Sustainable Development. Wan, J., Gu, J., Zhao, Q., Liu, Y., 2016. OPEN COD capture : a feasible option towards energy self-sufficient domestic wastewater treatment. Nat. Publ. Gr. 1–9. https://doi.org/10.1038/srep25054 SECTION II: CHANGING THE PARADIGM OF WASTEWATER TREATMENT 276 Wernet, G., Bauer, C., Steubing, B., Reinhard, J., Moreno-Ruiz, E., Weidema, B., 2016. The ecoinvent database version 3 (part I): overview and methodology. Int. J. Life Cycle Assess. 21, 1218–1230. https://doi.org/ 10.1007/s11367-016-1087-8 World Bank, 2019. Urban Development [WWW Document]. Zang, Y., Li, Y., Wang, C., Zhang, W., Xiong, W., 2015. Towards more accurate life cycle assessment of biological wastewater treatment plants: A review. J. Clean. Prod. 107, 676–692. https://doi.org/10.1016/j.jclepro.2015.05.060 Zeeman, G., Kujawa, K., de Mes, T., Hernandez, L., de Graaff, M., Abu-Ghunmi, L., Mels, A., Meulman, B., Temmink, H., Buisman, C., van Lier, J., Lettinga, G., 2008. Anaerobic treatment as a core technology for energy, nutrients and water recovery from source-separated domestic waste(water). Water Sci. Technol. 57, 1207–1212. https://doi.org/10.2166/wst.2008.101 GENERAL CONCLUSIONS AND FUTURE PERSPECTIVES 278 General conclusions and future perspectives The main objective of this doctoral thesis was to analyse and compare different wastewater treatment configurations from an environmental and economic point of view. This topic is in line with the growing concern to alleviate the effects related to climate change and water scarcity caused by anthropogenic activities and population growth. In this sense, WWTPs should be included in the philosophy of the circular economy and have emerged as a solution to recover products such as energy, nutrients and reclaimed water. In this context, two innovative strategies for wastewater treatment were evaluated: (i) one for centralised systems (Chapter 2 to Chapter 6) and (ii) one based on decentralised wastewater treatment schemes (Chapter 7 and Chapter 8). It was demonstrated that environmental impact methodologies and economic indicators provide useful information to assist the integration of these wastewater treatment strategies. The main findings and conclusions drawn from the different sections that make up this thesis are presented below: Section I: Improving centralised wastewater treatment systems. The main objective is to create a virtual wastewater treatment plant that encompasses the best technologies from an environmental and economic point of view for centralised systems. The conceptual design of a "virtual plant" will be based on the analysis developed from Chapter 2 to Chapter 6 in the framework of five different studies detailed below. In Chapter 2, AD technology was analysed at different scales with the main objective of assessing the environmental and economic viability of this technology. This treatment can be a good alternative for treating sludge due to the reuse of biogas as heat or energy as well as the potential of the digestate as a biofertiliser. In addition, if the amount of sludge is not very high, there are alternatives to improve the production yield of biogas such as the co-digestion of sewage sludge with food waste from households, services or even from the agro-food sector. Therefore, this technology will be included in the "virtual plant" as this chapter showed its efficiency. Despite the environmental and economic advantages of AD, CONCLUSIONS 279 sludge treatment can be a slow process. As mentioned in the introduction and in Chapter 3, hydrolysis, an initial stage in the AD process, is a limiting step, so in order to improve this unit and save treatment time, two alternative pre-treatments were proposed: chemical and thermal hydrolysis. In this case, the pre-treatments proved to be a good alternative to accelerate the hydrolysis stage and improve biogas production. It is true that the consumption of electricity and chemicals worsens the environmental profile but, it can be compensated with the increase in biogas production. This means that pre-treatments can also be a good alternative for the "virtual plant". However, these processes are still under development, and more information is needed to incorporate these pre-treatments into a real sludge line. In Chapter 4 and 5, treatment schemes at different scales were proposed to treat wastewater in a carbon neutral perspective. In Chapter 4, the WWTP scale is 100,000 equivalent inhabitants and in Chapter 5, the WWTPs scales are for 265,000 and 1,000,000 of equivalent inhabitants. As a summary, Figure 10.1 shows the results for different scenarios and different plant sizes. This figure may indicate the trend that plants should follow to have more environmentally friendly and economically viable schemes in centralised WWTPs. Thus, a priori, for large plants, the conventional scheme (PC + CAS) is the worst scheme due to the high energy consumption of the CAS unit, and there is less biogas production than in the other scenarios. The case of RBF + CEPT + IFAS that was incorporated in the smaller plant (100,000 equivalent inhabitants) is interesting. Although, there is a reduction in aeration due to the incorporation of IFAS technology it is not appropriate due to the consumption of chemicals in the primary treatment. This incorporation of the chemical can increase the environmental profile and economic impacts. For this reason, not all schemes are appropriate. The best solutions from an environmental and economic point of view and that can try to make plants carbon neutral are combinations based on UASB and IFAS as well as the HRAS and IFAS sequence. In the first case, the sludge line is not necessary, so this implies a reduction in land occupation and, in the UASB unit, biomass growth is slower than in aerobic units, so this implies a reduction in the amount of sludge. If this scheme is not possible, the HRAS unit allows a high OM recovery with a high methanisation factor CONCLUSIONS 280 while the subsequent IFAS stage provides advantages such as good nitrogen removal and low energy consumption (Figure 9.1). Figure 9.1. Different environmental and economic results for the wastewater treatment schemes studied. Bubbles represent the size of the plant and the colours correspond to different schemes. Orange: PC + CAS technologies, purple: RBF + CEPT+ IFAS, blue: UASB + IFAS, green: ERBF+ IFAS, and finally, turquoise: HRAS + IFAS Finally, Chapter 6 is related to the scale-up of an emerging technology. This chapter is very important in determining the minimum scale for reliable LCA and economic evaluation. In a context where decentralisation is becoming increasingly important, it is crucial to verify this methodology in the calculation of environmental impacts. This study can help to know whether the LCA approach makes sense in decentralised schemes. After conducting the study, the minimum volume that provides reliable environmental impacts was selected as 0.2 m3, while for economic indicators, the minimum scale was 1 m3. This means that when decentralised systems are studied, the volume needed to have consistent data will be 0.2 m3. Smaller scales may provide an unrealistic profile. -0.2 0.3 0.8 1.3 1.8 2.3 2.8 3.3 3.8 0 0.2 0.4 0.6 0.8 1 1.2 1.4 CC [kg CO2 eq/FU] Cost [€/FU] CONCLUSIONS 281 Section II: Changing the paradigm of wastewater treatment. This section consists of two chapters that focus on the possible advantages and disadvantages of different decentralised systems. Thus, as in the previous case, the main objective is to try to give a general approach. However, in this case it is more complicated than in the previous section because, the chapters are based on two different perspectives. First, a decentralised wastewater treatment plant based on a MBR unit for 2,000 inhabitants and located in Turkey was evaluated from an environmental point of view. In this case, the priory of the system was reused water in green areas because Turkey is a country with water deficit. For this propose, an indicator called AWARE was calculated. In addition, in this analysis, construction and operation phases were studied to quantify the environmental impacts related with the construction of the decentralised systems. With the objective of water reuse in mind, MBR is a technology that achieves satisfactory results on terms of water quality. Moreover, the water reuse had significant environmental impacts in all categories. Finally, for decentralised systems, the construction stage associated with the membrane fabrication can present high environmental impacts. Finally, Chapter 8 focuses on the point of view of the inhabitant. The study from the point of view of the inhabitant is very important because the citizen is increasingly aware that in a changing and continuously growing world, anthropogenic activities must ensure an exhaustive control of emissions and therefore lower carbon and water footprint values. Thus, this study compared a resident living in a centralised area with one living in a decentralised neighbourhood for wastewater treatment. The carbon footprint of a resident in terms of energy consumption can be reduced by 20-23% in areas that incorporate a decentralised system. Additionally, the water demand for green areas can be covered by reclaimed water. Therefore, there are no impacts related to water treatment and distribution. Finally, it is important to point out that these plants can be more flexible, and it is easy to recover resources, especially in countries where there are pressing problems of water scarcity. Therefore, these systems can also be a good option for new buildings or residential areas.